Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Postprandial amino acid, glucose and insulin responses among healthy adults after a single intake of Lemna minor in comparison with green peas: A randomised trial
    Zeinstra, Gertrude G. ; Somhorst, Dianne ; Oosterink, Els ; Fick, Henriette ; Klopping-Ketelaars, Ineke ; Meer, Ingrid M. Van Der; Mes, Jurriaan J. - \ 2019
    Journal of Nutritional Science 8 (2019). - ISSN 2048-6790
    Duckweed - Glucose - Human trials - Insulin - Lemna minor - Plant-based protein - Safety

    A high protein content combined with its enormous growth capacity make duckweed an interesting alternative protein source, but information about postprandial responses in humans is lacking. The present study aimed to assess the postprandial serum amino acid profile of Lemna minor in healthy adults in comparison with green peas. A secondary objective was to obtain insights regarding human safety. A total of twelve healthy volunteers participated in a randomised, cross-over trial. Subjects received two protein sources in randomised order with a 1-week washout period. After an overnight fast, subjects consumed L. minor or peas (equivalent to 20 g of protein). After a baseline sample, blood samples were taken 15, 30, 45, 60, 75, 90, 120, 150 and 180 min after consumption to assess amino acid, glucose and insulin levels. Heart rate, blood pressure and aural temperature were measured before and after consumption, and subjects reported on gastrointestinal discomfort for four subsequent days. Compared with green peas, significantly lower blood concentrations of amino acids from L. minor were observed, indicating lower digestibility. L. minor consumption resulted in lower plasma glucose and insulin levels compared with peas, probably due to different glucose content. There were no significant differences concerning the assessed health parameters or the number of gastrointestinal complaints, indicating that a single bolus of L. minor-grown under controlled conditions-did not induce acute adverse effects in humans. Further studies need to investigate effects of repeated L. minor intake and whether proteins purified from L. minor can be digested more easily.

    Slowly biodegradable organic compounds impact the biostability of non-chlorinated drinking water produced from surface water
    Hijnen, W.A.M. ; Schurer, R. ; Bahlman, J.A. ; Ketelaars, H.A.M. ; Italiaander, R. ; Wal, A. van der; Wielen, P.W.J.J. van der - \ 2018
    Water Research 129 (2018). - ISSN 0043-1354 - p. 240 - 251.
    AOC-A3 - AOC-P17/Nox - Biopolymers - Biostability of drinking water - Regrowth - Slowly biodegradable compounds
    It is possible to distribute drinking water without a disinfectant residual when the treated water is biologically stable. The objective of this study was to determine the impact of easily and slowly biodegradable compounds on the biostability of the drinking water at three full-scale production plants which use the same surface water, and on the regrowth conditions in the related distribution systems. Easily biodegradable compounds in the drinking water were determined with AOC-P17/Nox during 2012–2015. Slowly biodegradable organic compounds measured as particulate and/or high-molecular organic carbon (PHMOC), were monitored at the inlet and after the different treatment stages of the three treatments during the same period. The results show that PHMOC (300–470 μg C L−1) was approximately 10% of the TOC in the surface water and was removed to 50–100 μg C L−1. The PHMOC in the water consisted of 40–60% of carbohydrates and 10% of proteins. A significant and strong positive correlation was observed for PHMOC concentrations and two recently introduced bioassay methods for slowly biodegradable compounds (AOC-A3 and biomass production potential, BPC14). Moreover, these three parameters in the biological active carbon effluent (BACF) of the three plants showed a positive correlation with regrowth in the drinking water distribution system, which was assessed with Aeromonas, heterotrophic plate counts, coliforms and large invertebrates. In contrast, the AOC-P17/Nox concentrations did not correlate with these regrowth parameters. We therefore conclude that slowly biodegradable compounds in the treated water from these treatment plants seem to have a greater impact on regrowth in the distribution system than easily biodegradable compounds.
    Moderate alcohol consumption after a mental stressor attenuates the endocrine stress response
    Schrieks, I.C. ; Joosten, M.M. ; Klöpping-Ketelaars, W.A.A. ; Witkamp, R.F. ; Hendriks, H.F.J. - \ 2016
    Alcohol 57 (2016). - ISSN 0741-8329 - p. 29 - 34.
    Alcohol - Cortisol - Immune system - Psychological stress - Trier Social Stress Test

    Alcohol is often consumed to reduce tension and improve mood when exposed to stressful situations. Previous studies showed that moderate alcohol consumption may reduce stress when alcohol is consumed prior to a stressor, but data on the effect of alcohol consumption after a mental stressor is limited. Therefore, our objective was to study whether moderate alcohol consumption immediately after a mental stressor attenuates the stress response. Twenty-four healthy men (age 21–40 y, BMI 18–27 kg/m2) participated in a placebo-controlled trial. They randomly consumed 2 cans (660 mL, ∼26 g alcohol) of beer or alcohol-free beer immediately after a mental stressor (Stroop task and Trier Social Stress Test). Physiological and immunological stress response was measured by monitoring heart rate and repeated measures of the hypothalamic-pituitary-adrenal axis (HPA-axis), white blood cells and a set of cytokines. After a mental stressor, cortisol and adrenocorticotropic hormone (ACTH) concentrations were 100% and 176% more reduced at 60 min (P = 0.012 and P = 0.001, respectively) and 92% and 60% more reduced at 90 min (P

    New growing media and value added organic waste processing
    Blok, C. ; Rijpsma, E. ; Ketelaars, J.J.M.H. - \ 2016
    Acta Horticulturae 1112 (2016). - ISSN 0567-7572 - p. 269 - 280.
    Biochar - Charification - Compost - Container plants - Peat alternatives - Torrefaction

    Public pressure to use peat alternatives in horticultural rooting media offers room for the re-use of local organic waste materials. The re-use of organic wastes requires value added processing such as composting, co-composting, digestion, fractioning/sieving, pressing, binding, stabilising by torrefaction and charification, washing and nutrient exchange. Three cases are presented. In case 1, the new growing media project showed a successful reduction of peat in potting soil mixes at nurseries of 15 plant species. Peat use decreased from 78 to 27%-v/v. The 51%-v/v extra peat alternatives used were, averaged over all mixes used, 24%-v/v coir products, 13%-v/v wood fibre, 6%-v/v bark products and 2%-v/v for each of compost, rice husks, perlite or rockwool granulate. When compared to the standard control mixes yield decreased for two species, increased for two species and was equal for the remaining species. Important, sometimes limiting, properties were stability, nitrogen fixation, EC level, sodium level, rewetting rate and water holding capacity. In case 2 torrefaction at 250°C was used to turn a fast degrading nitrate fixing reed (Phragmites australis) into a non-toxic potting soil constituent which could be added to potting soil mixes up to 80%-v/v. In case 3 the cation exchange complex of coir was measured and saturated with calcium ions. The amount and concentration of a solution necessary to exchange sodium and potassium was 600 meq kg-1 and was dosed as 10 L of 30 mmol L-1 calcium nitrate. In all 3 cases product quality measurements and adapted processing or cultivation practises were discussed. A set of the most important measurements is presented, including: pH, EC, EC level, sodium level, potassium level, stability, nitrogen fixation, easily available water and rewetting rate. In conclusion additional or adapted processing of organic waste guided by proper measurements can increase the value of such organic waste for use in horticulture.

    Smart Seafood
    Ketelaars, J.J.M.H. ; Tacken, W. - \ 2014
    zout water - voedselproductie - nieuwe producten - zoutwaterlandbouw - landbouw - nieuwe voedingsmiddelen - alternatieve landbouw - teelt - saline water - food production - new products - saline agriculture - agriculture - novel foods - alternative farming - cultivation
    Met de slogan ‘Land in Zee’ profileert de provincie Zeeland zich als de plek waar de zee altijd en overal dichtbij is. Die nabijheid nodigt uit om te profiteren van de unieke mogelijkheden van zoutwater voor recreatie en natuur, maar ook voor de productie van voedsel. Met het programma Smart Seafood wil de provincie slim gebruik van zoutwater en zilte omstandigheden binnendijks bevorderen. Dat kan door kennis en kennisontwikkeling te verbinden met ondernemerschap. Waar liggen de kansen voor nieuwe producten uit een zout of zilt milieu?
    Toekomstperspectief voor het gemengd zilt bedrijf
    Ketelaars, J.J.M.H. ; Ruizeveld de Winter, A.C. - \ 2014
    Wageningen : Plant Research International, Business Unit Agrosyteemkunde (Rapport / Plant Research International 545) - 66
    zoutwaterlandbouw - landbouw - toekomst - visteelt - aquacultuur - agrarische economie - zeeland - haalbaarheidsstudies - economische haalbaarheid - saline agriculture - agriculture - future - fish culture - aquaculture - agricultural economics - zeeland - feasibility studies - economic viability
    Op het Proefbedrijf Zeeuwse Tong in Colijnsplaat is gedurende vier jaren (2010-2013) ervaring opgedaan met de kweek van zagers, tong, algen, en schelpdieren, waaronder tapijtschelpen, Japanse oesters en platte oesters. In onderstaande worden de belangrijkste ervaring en met de verschillende teelten afzonderlijk en in combinatie samengevat. Vervolgens komen aan bod: de technische en economische haalbaarheid, en de risico’s en onzekerheden.
    Perspectief voor binnendijkse kweek
    Ketelaars, J.J.M.H. - \ 2013
    Goes : Stichting Zeeuwse Tong - 65
    aquacultuur - zoutwaterlandbouw - visteelt - agropisciculture - zeeland - zout water - tong (vis) - algen - schaaldieren - oesters - mossels - haalbaarheidsstudies - aquacultuursystemen - aquaculture - saline agriculture - fish culture - agropisciculture - zeeland - saline water - dover soles - algae - shellfish - oysters - mussels - feasibility studies - aquaculture systems
    In 2009 startte Stichting Zeeuwse Tong een vijfjarig proefproject met als doel: 1. op praktijkschaal technische en economische kennis te verzamelen van binnendijkse zoutwateraquacultuur, in het bijzonder van de productie van tong, zagers, algen, schelpdieren en zilte gewassen, en 2. om deze kennis beschikbaar te maken voor geïnteresseerde ondernemers. De motivatie voor het Proefproject is tweeledig: 1. kansen benutten voor zoutwateraquacultuur gezien de toenemende vraag naar en interesse in zeevoedsel, 2. alternatieven ontwikkelen voor het gebruik van landbouwgrond die toenemende hinder ondervindt van verzilting. Deze rapportage geeft een samenvatting van de belangrijkste R&D-resultaten. Tegen deze achtergrond worden vervolgens de technische en economische haalbaarheid, de risico’s en onzekerheden besproken van de verschillende teelten of bedrijfsvormen.
    Zeeuwse tong steeds dichter bij het bord
    Ketelaars, J.J.M.H. - \ 2011
    Kennis Online 2011 (2011)14 juni. - p. 14 - 14.
    visteelt - aquacultuur - schaal- en schelpdierenteelt - solea - tong (vis) - proefbedrijven - zeeland - fish culture - aquaculture - shellfish culture - solea - dover soles - pilot farms - zeeland
    De Nederlandse overheid heeft samen met het bedrijfsleven vijftien miljoen euro geïnvesteerd in het project Zeeuwse tong. De proefboerderij die dit jaar zijn eerste tong moet gaan afleveren, moet de start zijn van een hele nieuwe bedrijfstak: zilte gemengde teelt van vis en groenten.
    Zitle Teelt: Eerste zagers gaan begin mei in de kweekbassins - Proefbedrijf Zeeuwse Tong bijna klaar voor productie ( interview met W. Brandenburg en J. Ketelaars)
    Jansen, B. ; Brandenburg, W.A. ; Ketelaars, J.J.M.H. - \ 2010
    Provinciale Zeeuwse Courant (2010).
    Colonization of torrefied grass fibers by plant beneficial microorganisms
    Trifonova, R.D. ; Babini, V. ; Postma, J. ; Ketelaars, J.J.M.H. ; Elsas, J.D. van - \ 2009
    Applied Soil Ecology 41 (2009)1. - ISSN 0929-1393 - p. 98 - 106.
    pythium damping-off - serratia-plymuthica - pseudomonas-corrugata - rhizoctonia-solani - biological-control - biocontrol strain - soil - suppression - bacterial - rot
    This study aimed to assess the colonization of thermally treated (i.e. torrefied) grass fibers (TGFs), a new prospective ingredient of potting soil. Eleven bacterial strains and one fungus, Coniochaeta ligniaria F/TGF15, all isolated from TGF or its extract after inoculation with a soil microbial community, were tested for their ability to colonize TGF. Surprisingly, none of these bacteria were able to directly colonize TGF either as single inoculants or as a consortium. Furthermore, bacterial persistence or growth in TGF was not improved by the addition of nutrients or a surfactant. Only extensive washing of the substrate, presumably removing bacteriostatic or bactericidal compounds, allowed bacterial growth on the fibers. Strikingly, the fungal strain consistently colonized TGF up to high densities (up to 1010 CFU per g dry TGF). Given the unique capacity of this fungus to degrade toxic compounds including phenols, TGF was colonized with it for different periods of time, after which a consortium of seven selected bacterial isolates was added. Co-presence of the fungus, or 3 and 24 h pre-colonization with it, was insufficient to create a habitable environment for the bacterial consortium. However, fungal pre-colonization of minimally 3 days allowed the bacterial consortium to colonize the TGF at numbers up to 109 to 1010 CFU per g dry substrate. The resultant bacterial community consisted of at least four strains, i.e. Pseudomonas putida 15/TGE5, Serratia plymuthica 23/TGE5, Pseudomonas corrugata 31/TGE5, and Methylobacterium radiotolerans 56/TGF10, as shown by PCR of colonies on plates and PCR–DGGE profiling. Two persisters, S. plymuthica 23/TGE5 and P. corrugata 31/TGE5, were highly antagonistic towards several phytopathogenic fungi. Thus, a microbial community with plant-beneficial potential was established on TGF, provided that the fungus C. ligniaria F/TGF15 first creates habitable space in the matrix
    Removal of phytotoxic compounds from torrefied grass fibres by plant-beneficial microorganisms
    Trifonova, R.D. ; Postma, J. ; Verstappen, F.W.A. ; Bouwmeester, H.J. ; Ketelaars, J.J.M.H. ; Elsas, J.D. van - \ 2008
    FEMS microbiology ecology 66 (2008)1. - ISSN 0168-6496 - p. 158 - 166.
    mill waste-water - escherichia-coli - phenolic removal - laccase activity - growth - strain - peat - detoxification - fermentation - enzyme
    We aimed to select microorganisms colonizing torrefied grass fibres (TGF) and simultaneously reducing the phytotoxicity which appeared after heat treatment of the fibres. Eighty-eight bacterial strains and one fungus, previously isolated from a sequential enrichment experiment on torrefied fibres and extracts, were tested separately for their capacity to decrease phytotoxicity. Eleven of the bacterial strains and the fungus significantly reduced phytotoxicity. These organisms were checked for their ability to grow on agar containing phenol, 2-methoxyphenol, 2,6-dimethoxyphenol, 2-furalaldehyde, pyrrole-2-carboxaldehyde and furan-2-methanol as sole carbon sources. The fungus F/TGF15 and the bacterial strain 66/TGF15 were able to grow on all six compounds. Strains 15/TGE5, 23/TGE5, 43/TGE20, 56/TGF10 and 95/TGF15 grew on two to four compounds, and strain 72/TGF15 only on one compound. Strains 31/TGE5, 34/TGE5, 48/TGE20 and 70/TGF15 did not grow on any of the single toxic compounds. GC analyses of torrefied grass extracts (TGE) determined which compounds were removed by the microorganisms. F/TGF15 was the only isolate depleting phenol, 2-methoxyphenol, 2-dihydrofuranone and pyrrole-2,5-dione-3-ethyl-4-methyl. Strains 15/TGE5, 23/TGE5, 31/TGE5 and 56/TGF10, and the fungus depleted 2-furalaldehyde, 2-furan-carboxaldehyde-5-methyl, pyrrole-2-carboxaldehyde, 5-acetoxymethyl-2-furaldehyde and benzaldehyde-3-hydroxy-4-methoxy. These promising candidates for colonizing and simultaneously reducing the phytotoxicity of TGF were affiliated with Pseudomonas putida, Serratia plymuthica, Pseudomonas corrugata, Methylobacterium radiotolerans and Coniochaeta ligniaria.
    Thermally treated grass fibers as colonizable substrate for beneficial bacterial inoculum
    Trifonova, R.D. ; Postma, J. ; Ketelaars, J.J.M.H. ; Elsas, J.D. van - \ 2008
    Microbial Ecology 56 (2008)3. - ISSN 0095-3628 - p. 561 - 571.
    coconut coir dusts - sp-nov. - soil - methylobacterium - 4-chlorophenol - microorganisms - phytotoxicity - populations - sequence - removal
    This study investigates how thermally treated (i.e., torrefied) grass, a new prospective ingredient of potting soils, is colonized by microorganisms. Torrefied grass fibers (TGF) represent a specific colonizable niche, which is potentially useful to establish a beneficial microbial community that improves plant growth. TGF and torrefied grass extracts (TGE) were inoculated with a suspension of microorganisms obtained from soil. Sequential microbial enrichment steps were then performed in both substrates. The microbial communities developing in the substrates were assessed using cultivation-based and cultivation-independent approaches. Thus, bacterial isolates were obtained, and polymerase chain reaction¿denaturing gradient gel electrophoresis (DGGE) analyses for bacterial communities were performed. Partial sequencing of the 16S ribosomal RNA gene from isolates and bands from DGGE gels showed diverse communities after enrichment in TGE and TGF. Bacterial isolates affiliated with representatives of the ¿-proteobacteria (Methylobacterium radiotolerans, Rhizobium radiobacter), ¿-proteobacteria (Serratia plymuthica, Pseudomonas putida), Cytophaga¿Flavobacterium¿Bacteroides (CFB) group (Flavobacterium denitrificans), ß-proteobacteria (Ralstonia campinensis), actinobacteria (Cellulomonas parahominis, Leifsonia poae, L. xyli subsp. xyli, and Mycobacterium anthracenicum), and the firmicutes (Bacillus megaterium) were found. In TGE, ¿-proteobacteria were dominant (61.5% of the culturable community), and 20% belonged to the CFB group, whereas actinobacteria (67.4%) and ¿-proteobacteria (21.7%) were prevalent in TGF. A germination assay with lettuce seeds showed that the phytotoxicity of TGF and TGE decreased due to the microbial enrichment
    Prediction of fecal and urinary N excretion in dairy cattle
    Evert, F.K. van; Meer, H.G. van der; Ketelaars, J.J.M.H. - \ 2007
    In: Ammonia emissions in agriculture / Monteny, G.J., Hartung, E., Wageningen : Wageningen Academic Publishers - ISBN 9789086860296 - p. 91 - 93.
    Towards a dairy farm that produces more than milk
    Ketelaars, J.J.M.H. ; Evert, F.K. van; Rutgers, B. - \ 2006
    In: Changing European farming systems for a better future. New visions for rural areas,. - Wageningen : Wageningen Academic Publishers - ISBN 9789086860029 - p. 183 - 183.
    Fytotoxiciteit, nematotoxiciteit, en microbiele stabiliteit van getorreficeerd gras
    Zoon, F.C. ; Kok, C.J. ; Ketelaars, J.J.M.H. - \ 2006
    Wageningen : Plant Research International (Nota / Plant Research International 380) - 30
    groeimedia - plantenresten - grassen - phragmites - vezelgewassen - fytotoxiciteit - torrefactie - growing media - plant residues - grasses - phragmites - fibre plants - phytotoxicity - torrefaction
    Scheppen van ruimte : systeeminnovaties voor duurzame voedselproductie, werkplannen 2005
    Neeteson, J.J. ; Koops, A.J. ; Ketelaars, J.J.M.H. ; Vosman, B. ; Sijtsma, L. ; Wolfert, J. ; Kampers, F.W.H. - \ 2005
    Wageningen : Plant Research International (Nota Plant Research International 344) - 44 p.
    Scheppen van ruimte : systeeminnovaties voor duurzame voedselproductie, jaarverslag 2004
    Neeteson, J.J. ; Koops, A.J. ; Ketelaars, J.J.M.H. ; Vosman, B. ; Sijtsma, L. ; Wolfert, J. ; Kampers, F.W.H. - \ 2005
    Wageningen : Plant Research International (Nota / Plant Research International 343) - 44
    voedselproductie - systeemanalyse - innovaties - duurzaamheid (sustainability) - marketing van voedingsmiddelen - voedselvoorziening - microbiële eiwitten - landbouwontwikkeling - nederland - food production - systems analysis - innovations - sustainability - food marketing - food supply - microbial proteins - agricultural development - netherlands
    Ruimte wordt in toenemende mate een schaars goed. Zowel nationaal als mondiaal is er sprake van een gevecht om deze schaarse ruimte. Er zijn claims vanuit diverse hoeken waaronder landbouw, natuur en recreatie, energieproductie, stedelijke ontwikkeling en waterberging. Duurzame voedselproductie kan niet los gezien worden van duurzaam ruimtegebruik. Het programma Scheppen van Ruimte wil aan dit proces een bijdrage leveren. Het bestrijkt bewust een breed terrein van onderzoek vanuit de gedachte dat er geen unieke oplossing bestaat, maar dat de toekomst veelvormig zal zijn. Systeeminnovaties zijn daarom nodig om het ruimteconflict tussen de verschillende functies te verzachten. De voedselproductie-functie moet ruimte scheppen voor andere functies
    Nieuwe landbouw: inventarisatie van kansen
    Langeveld, J.W.A. ; Koops, A.J. ; Ketelaars, J.J.M.H. ; Marcelis, L.F.M. ; Hassink, J. ; Blom, M. ; Sanden, P.A.C.M. van de - \ 2005
    onbekend : PRI Agrosysteemkunde (Nota / Plant Research International 330) - 84
    landbouw - tuinbouw - teelt onder bescherming - biologische landbouw - natuurbescherming - bio-energie - non-food producten - landbouwproducten - zorgboerderijen - multifunctionele landbouw - biobased economy - biomassa productie - agriculture - horticulture - protected cultivation - organic farming - nature conservation - bioenergy - non-food products - agricultural products - social care farms - multifunctional agriculture - biobased economy - biomass production
    In opdracht van het Ministerie van LNV inventariseerde en evalueerde PRI de nieuwe productiekansen voor de Nederlandse plantaardige sectoren.Tevens doet PRI aanbevelingen voor beleid en onderzoek. Nieuwe landbouw is één van de projecten van het Transitieteam van het Ministerie. Behandelde thema's in dit rapport: landbouwgrondstoffen, zoutwater landbouw, kasteelt, sociale dienstverlening, ecologische dienstverlening, het nieuwe consumeren en Nederland regieland
    Serum carotenoids and vitamins in relation to markers of endothelial function and inflammation
    Broekmans, W. ; Klopping-Ketelaars, I.A.A. ; Bots, M.L. ; Kluft, C. ; Princen, H. ; Hendriks, H.F.J. ; Tijburg, L.B.M. ; Poppel, G. van; Kardinaal, A.F.M. - \ 2004
    European Journal of Epidemiology 19 (2004)10. - ISSN 0393-2990 - p. 915 - 921.
    coronary-heart-disease - low-density-lipoprotein - c-reactive protein - cardiovascular-disease - myocardial-infarction - beta-carotene - adhesion molecules - risk-factors - healthy-men - lycopene concentration
    Background: Endothelial cell dysfunction may be related to an increase in cellular oxidative stress. Carotenoids and vitamins could have an antioxidant-mediated tempering influence on endothelial function and inflammation, thereby reducing the risk of atherosclerosis. Methods: We measured serum carotenoids, alpha-tocopherol and Vitamin C concentrations in 379 subjects sampled from the general population. High-sensitive C-reactive protein (CRP), fibrinogen (Fbg) and leukocytes were measured as markers of inflammation. Furthermore, soluble intercellular adhesion molecule-1 (sICAM- 1) and flow-mediated vasodilation (FMD; n = 165) were measured as markers of endothelial function. Relationships between serum carotenoids and vitamins and markers of endothelial function and inflammation were analysed after adjustment for confounding. Results: In the total study group, lutein and lycopene were inversely related to sICAM- 1 with regression-coefficients of -0.38 +/- 0.19 (p = 0.04) and) 0.16 +/- 0.08 (p = 0.04) per 1 mumol/l, respectively. beta-Carotene was inverse related to leukocytes (-0.23 +/- 0.07; p = 0.007) and CRP (-1.09 +/- 0.30; p = 0.0003) per 1 mumol/l. Vitamin C was inverse related to CRP (-0.01 +/- 0.005; p = 0.04) per 1 mumol/l, whereas alpha-tocopherol was positively related to CRP (0.03 +/- 0.01; p = 0.02) per 1 mu/l. Zeaxanthin was inversely related to FMD (31.2 +/- 15.3; p = 0.04) per 1 mumol/l. Conclusion: The inverse relations between carotenoids, Vitamin C and sICAM- 1, CRP and leukocytes may help to explain the possible protective effect of carotenoids and Vitamin C on atherosclerosis through an influence on inflammatory processes and endothelial function.
    Scheppen van Ruimte: systeeminnovaties voor duurzame voedselproductie, werkplannen 2004
    Neeteson, J.J. ; Koops, A.J. ; Ketelaars, J.J.M.H. ; Loo, E.N. van; Vosman, B. ; Sijtsma, L. ; Wolfert, J. ; Kampers, F.W.H. - \ 2004
    Wageningen : Plant Research International (Nota / Plant Research International 289) - 28 p.
    Ketelaars, J.J.M.H. ; Doepel, D. - \ 2004
    In: Zee in zicht. Zilte waarden duurzaam benut / Luiten, Esther, Den Haag : STT/Beweton - ISBN 9789080449688 - p. 160 - 169.
    Mariene parken : duurzaam in zee
    Broeze, J. ; Simons, A.E. ; Ketelaars, J.J.M.H. ; Bethe, F.H. ; Olde Loohuis, R.J.W. ; Graaf, J. de; Doepel, D. ; Wilt, J.G. de - \ 2004
    Den Haag : InnovatieNetwerk Groene Ruimte en Agrocluster (Rapport / InnovatieNetwerk Groene Ruimte en Agrocluster : Serie achtergrondrapporten nr. 04.2.070) - ISBN 9789050592178 - 36
    mariene gebieden - marien milieu - ruimtelijke ordening - landgebruiksplanning - economische ontwikkeling - nederland - marine areas - marine environment - physical planning - land use planning - economic development - netherlands
    Rapport bevat de bijdragen: State-of-the-art van voedselproductiesystemen; Gesloten productiesystemen: Atlantis 2020; Luwteparken: nieuwe functiecombinaties in kalm water
    Conserveermiddelen on-line
    Top, J.L. ; Ketelaars, N.J.J.P. ; Hulzebos, J.L. - \ 2004
    Voedingsmiddelentechnologie 37 (2004)4. - ISSN 0042-7934 - p. 27 - 27.
    conserveermiddelen - voedselconserveermiddelen - voedselindustrie - eigenschappen - databanken - voedingsstoffendatabanken - informatiesystemen - internet - preservatives - food preservatives - food industry - properties - databases - nutrient databanks - information systems - internet
    Antimicrobials Online is een Engelstalige database die wetenschappelijke informatie over natuurlijke conserveermiddelen via internet beschikbaar stelt aan de levensmiddelenindustrie. Het project is uitgevoerd door Wageningen UR-Agrotechnology & Food Innovations. Er volgt uitbreiding met traditionele voedingsmiddelen
    Soluble intercellular adhesion molecule 1 and flow-mediated dilatation are related to the estimated risk of coronary heart disease independently from each other
    Witte, D.R. ; Broekmans, W. ; Kardinaal, A.F.M. ; Klopping-Ketelaars, I.A.A. ; Poppel, G. van; Bots, M.L. ; Kluft, C. ; Princen, J.M.G. - \ 2003
    Atherosclerosis 170 (2003)1. - ISSN 0021-9150 - p. 147 - 153.
    endothelium-dependent vasodilation - hemodialysis-patients - postmenopausal women - hdl-cholesterol - artery disease - healthy-men - dysfunction - atherosclerosis - markers - plasma
    Background: Flow mediated dilatation (FMD) of the brachial artery and soluble intercellular adhesion molecule 1 (sICAM-1) are measures of distinct functions of the endothelium, reflecting nitric oxide (NO)-mediated and pro-inflammatory status, respectively. The comparative value of the two measures in relation to cardiovascular risk is unknown. Objective: To study and quantify the relation between these two measures, and their relative value in relation to the risk of coronary heart disease as estimated by the Framingham risk function. Methods: We performed a single centre population-based study of 85 men and 81 women, aged 18¿73 years. Endothelial function was assessed biochemically by sICAM-1 and functionally by FMD. In addition traditional cardiovascular risk factors, CRP, leukocyte count, homocysteine and fibrinogen were determined. Analyses were performed with multivariate linear regression, adjusted for age, gender, and CRP. Results: Median sICAM-1 levels were 217.0 ¿g/l (interquartile range: 174.0¿348.5). Mean FMD was 4.5% (S.D.: 3.9). The regression coefficient for the association between sICAM-1 and FMD was ¿3.3 ¿g/l (95% CI: ¿6.0;¿0.6) per percentage rise in FMD, after adjustment for age, gender, smoking, oral contraceptives (OC) use, classical risk factors and CRP. After adjustment for CRP and sICAM-1, the estimated risk of coronary heart disease in the next 10 years varied from 1.55% (95%CI: 0.89; 2.70) in the highest quintile of FMD to 3.92% (95% CI: 2.23; 6.92) in the lowest quintile. For sICAM-1, estimated risk, adjusted for FMD and CRP varied from 1.50% (95%CI: 0.85; 2.64) in the lowest quintile of sICAM-1 to 4.15% (95%CI: 2.35; 7.34) in the highest quintile. P-values for trends were 0.02 and 0.01 for quintiles of FMD and quintiles of sICAM-1, respectively. Conclusion: These findings indicate that sICAM-1 and FMD are related in healthy individuals, independently of cardiovascular risk factors and CRP, and that they are both related to the estimated risk of coronary heart disease, independently of each other.
    Decreased carotenoid concentrations due to dietary sucrose polyesters do not affect possible markers of disease risk in humans
    Broekmans, W. ; Klopping-Ketelaars, I.A.A. ; Weststrate, J.A. ; Tijburg, L.B.M. ; Poppel, G. van; Vink, A.A. ; Berendschot, T.T.J.M. ; Bots, M.L. ; Castenmiller, W.A.M. ; Kardinaal, A.F.M. - \ 2003
    The Journal of Nutrition 133 (2003)3. - ISSN 0022-3166 - p. 720 - 726.
    macular pigment density - light-induced erythema - beta-carotene - serum concentrations - olestra consumption - epidemiologic evidence - tissue concentrations - fragment 1+2 - vitamin-e - plasma
    Excessive consumption of energy and fat increases the risk for obesity. Snacks containing sucrose polyesters (SPE) as a dietary fat replacer are on the market in the United States. SPE products have been shown to lower concentrations of serum carotenoids in short-term studies. Experimental studies on the longer-term effects on health of decreased carotenoid concentrations are lacking. A 1-y randomized, double-blind, placebo-controlled parallel trial was performed. Subjects (n = 380) with a habitual low or high fruit and vegetable intake were assigned to the treatments (0, 7, 10 or 17 g/d SPE). SPE was given in the form of spreads, chips or both. The groups were compared for serum carotenoids, vitamins and markers of oxidative damage, eye health, cardiovascular health and immune status. After 1 y, serum lipid-adjusted carotenoids showed the largest decrease in the SPE chips and spread group (17 g/d) compared with the control group [-carotene 33%; ß-carotene 31%, lycopene 24%, ß-cryptoxanthin 18%, lutein 18% (all P <0.001) and zeaxanthin 13% (P <0.05)]. Consumption of SPE spread (10 g/d SPE) decreased carotenoid concentrations by 11¿29% (all P <0.05). SPE chips (7 g/d SPE) decreased zeaxanthin (11%), ß-carotene (12%) and -carotene (21%; all P <0.05). Serum lipid adjusted -tocopherol decreased significantly by 6¿8% (all P <0.001) in all SPE groups. No negative effects were observed on markers of oxidation, eye health, cardiovascular health or immune status. This study shows that decreases in serum carotenoid concentrations do not affect possible markers of disease risk.
    Scheppen van Ruimte: systeeminnovaties voor duurzame voedselproductie, werkplannen 2003
    Neeteson, J.J. ; Koops, A.J. ; Ketelaars, J.J.M.H. ; Loo, E.N. van; Vosman, B. ; Eggink, G. ; Sijtsma, L. ; Wolfert, J. - \ 2003
    Wageningen : Plant Research International (Nota / Plant Research International 229) - 52 p.
    Scheppen van Ruimte: systeeminnovaties voor duurzame voedselproductie, programma-tekst
    Neeteson, J.J. ; Koops, A.J. ; Ketelaars, J.J.M.H. ; Loo, E.N. van; Vosman, B. ; Eggink, G. ; Sijtsma, L. ; Wolfert, J. - \ 2003
    Wageningen : Plant Research International (Nota / Plant Research International 228) - 30 p.
    Scheppen van Ruimte: systeeminnovaties voor duurzame voedselproductie, jaarverslag 2003
    Neeteson, J.J. ; Koops, A.J. ; Ketelaars, J.J.M.H. ; Loo, E.N. van; Vosman, B. ; Sijtsma, L. ; Wolfert, J. ; Kampers, F.W.H. - \ 2003
    Wageningen : Plant Research International (Nota / Plant Research International 288) - 40 p.
    Hoezo, een bedrijfsmatige zorgboerderij? : een conceptuele verkenning
    Ketelaars, D. - \ 2003
    Wageningen : Wetenschapswinkel Wageningen UR (Rapport / Wetenschapswinkel Wageningen UR 194a) - ISBN 9789067547017 - 38 p.
    economische haalbaarheid - nederland - zorgboerderijen - multifunctionele landbouw - economic viability - netherlands - social care farms - multifunctional agriculture
    De bodem onder de zorgboerderij : naar een onderbouwing van de heilzame eigenschappen van een zorgboerderij
    Hassink, J. ; Ketelaars, D. - \ 2003
    In: Handboek Dagbesteding Wageningen : Plant Research International - p. 1 - 25.
    zorgboerderijen - werkwijze - effecten - sociale structuur - persoonlijke ontwikkeling - stimulansen - agrarische bedrijfsvoering - sociale zorg - social care farms - mode of action - effects - social structure - personal development - incentives - farm management - social care
    Onderzoek naar de werking van zorgboerderijen. Geconcludeerd wordt dat een zorgboerderij een kansrijke plek is om persoonlijke groei en ontwikkeling van cliënten mogelijk te maken. Het is een omgeving die prikkelt en stimuleert en daarnaast voldoende structuur en veiligheid kan bieden opdat cliënten de uitdaging ook aan durven gaan. Een zorgboerderij is ook een omgeving met voldoende ruimte om elkaar niet in de weg te zitten en voldoende variatie om werk of dagbesteding op-maat te bieden. De diversiteit in werkzaamheden en de activering van alle zintuigen, de structuur en het ritme dat een zorgboerderij kan bieden, het levert allemaal een bijdrage aan de gelegenheid voor cliënten om veiligheid, uitdaging en verbinding te ervaren
    FARMMIN: Modeling Crop-Livestock Nutrient Flows
    Evert, F.K. van; Berge, H.F.M. ten; Meer, H.G. van der; Rutgers, B. ; Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2003
    Imaging spectroscopy for grassland management
    Schut, A.G.T. ; Ketelaars, J.J.M.H. ; Lokhorst, C. - \ 2003
    In: 1 st European Conference on Precision livestock farming, Berlin - p. 155 - 160.
    Assessment of seasonal dry-matter yield and quality of grass swards with imaging spectroscopy
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2003
    Grass and Forage Science 58 (2003)4. - ISSN 0142-5242 - p. 385 - 396.
    The potential of imaging spectroscopy for the assessment of seasonal dry-matter (DM) yield and sward quality was studied. Relationships between spatial heterogeneity of tiller density, light interception, ground cover and seasonal DM yield were developed. Sward heterogeneity was quantified by the spatial standard deviation of ground cover and of logarithmically transformed ground cover, and patterns in ground cover transects were quantified by wavelet entropy. An experiment was conducted with eight control (C) swards, eight naturally damaged (ND) swards and twelve artificially damaged (AD) swards. Swards were established in containers and spectroscopic images were recorded twice weekly. Seasonal DM yield was linearly related to a combination of means of ground cover and index of reflection intensity (r2 = 0.93). Spatial variation of tiller density was larger for AD and ND swards than for C swards. Values of the spatial standard deviation of ground cover and wavelet entropy were larger for AD and ND swards than for C swards. A single spatial standard deviation of ground cover value of 13% discriminated ND and AD swards from C swards. Seasonal means of wavelet entropy (r2 = 0.70) and the spatial standard deviation of ground cover (r2 = 0.63) at harvest were linearly related to seasonal DM yield. It is concluded that imaging spectroscopy can be used for assessing seasonal DM yield and sward heterogeneity.
    Determinants of skin sensitivity to solar irradiation
    Broekmans, W. ; Vink, A.A. ; Boelsma, E. ; Klöpping-Ketelaars, W.A.A. ; Tijburg, L.B.M. ; Veer, P. van 't; Poppel, G. van; Kardinaal, A.F.M. - \ 2003
    European Journal of Clinical Nutrition 57 (2003). - ISSN 0954-3007 - p. 1222 - 1229.
    basal-cell carcinoma - light-induced erythema - beta-carotene - vitamin-e - serum concentrations - alpha-tocopherol - clinical-trial - ascorbic-acid - hair color - dna-damage
    Background: Acute effects of UV irradiation include UV-induced erythema. Sunlight plays an important role in the development of skin cancer. Several predictive factors of UV-induced erythema could also be predictive for skin cancer. Objective: Our objective was to quantitatively assess phenotypical and nutritional determinants of sensitivity to UV irradiation, as assessed by the minimal erythema dose (MED). Design: We conducted a cross-sectional study among 335 volunteers. Sensitivity to UV irradiation was established through assessment of the MED. Phenotypical determinants, including skin melanin content, hair color and iris color were determined by skin reflectance spectrometry, a subjective questionnaire and an objective classification system, respectively. Furthermore, dietary exposure was measured by carotenoids, vitamin C, retinol and alpha-tocopherol in serum. Results: Male subjects were found to be more sensitive to UV irradiation; that is, the MED was significantly lower compared to female subjects. Skin melanin content, which was positively associated with iris color in both sexes and with hair color in men, was the main phenotypical determinant of sensitivity to UV irradiation. No associations were found between serum carotenoids and MED in the total study group. Vitamin C was inversely associated with MED. However, associations between carotenoids concentrations and MED showed a positive trend in subjects with melanin values above and a negative trend in subjects below the median after adjustment for gender and total cholesterol. Conclusions: Skin melanin content and gender are important determinants of sensitivity to UV irradiation. No relation was found between serum carotenoids and MED in the total study group. The inverse association between vitamin C and MED was against our hypothesis. For the modifying effect of melanin on the association between carotenoids and MED, we do not have a clear biological explanation.
    Monitoring grass swards using imaging spectroscopy
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2003
    Grass and Forage Science 58 (2003)3. - ISSN 0142-5242 - p. 276 - 286.
    estimating herbage mass - rising-plate meter - capacitance meter - pastures - reflectance
    The potential of an imaging spectroscopy system with high spatial (0.16-1.45 mm2) and spectral resolution (5-13 nm) was explored for monitoring light interception and biomass of grass swards. Thirty-six Lolium perenne L. mini-swards were studied for a total of eleven consecutive growth periods. Hyperspectral images and light interception (LI) were recorded twice weekly. On two dates ground cover was scored visually (GCV). At harvest, leaf area index (LAI), fresh-matter yield and dry-malter yield (DMY) were determined. Classification of images yielded several estimates of the image ground cover (GCi) and the index of reflection intensity (IRI). The GCi was highly correlated with GCV (r adj2 = 0.94), LAI (radj2 = 0.88) and LI (radj2 = 0.95, for dense swards under cloudy skies). However, the relationship between GCi and LI depended on sky conditions and sward structure. Under cloudy skies, LI was linearly related to GCi, whereas under clear skies, this relation was logistic. Regression analysis of GCi and yields showed correlations with r adj2 of between 0.75 and 0.82. The mean error of DMY estimates was 340 kg. In conclusion, estimates of GCi and IRI can be used to predict DMY, even for high yield levels (up to 3500 kg DM ha -1), allowing accurate, non-destructive monitoring of biomass and light interception of grass swards.
    Comparison of grass sward dry matter yield assessment with imaging spectroscopy, disk plate meter and Cropscan
    Schut, A.G.T. ; Ketelaars, J.J.M.H. ; Hendriks, M.M.W.B. ; Kornet, J.G. ; Lokhorst, C. - \ 2003
    In: Precision livestock farming Wageningen : Wageningen Academic Publishers - ISBN 9789076998220 - p. 149 - 154.
    Early detection of drought stress in grass swards with imaging spectroscopy
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2003
    NJAS Wageningen Journal of Life Sciences 51 (2003)3. - ISSN 1573-5214 - p. 319 - 337.
    grasveld - lolium perenne - droogte - stress - spectroscopie - spectrometrie - reflectiefactor - grass sward - lolium perenne - drought - stress - spectroscopy - spectrometry - reflectance - grown perennial ryegrass - leaf water status - spectral reflectance - red edge - leaves - vegetation - cotton
    The potential of an experimental imaging spectroscopy system with high spatial (0.28-1.45 mm2) and spectral (5-13 nm) resolution was explored for early detection of drought stress in grass. A climate chamber experiment was conducted with nine Lolium perenne L. mini swards with drought stress treatments at two nitrogen levels. Images were recorded once every two days. Growth was monitored by changes in ground cover (GC), index of reflection intensity (IRI) and wavelength position of and gradient at inflection points, as estimated from images. Drought stress increased leaf dry matter and sugar content. Drought stress decelerated and ultimately reversed GC evolution, and kept IRI at low values. In contrast to unstressed growth, all absorption features narrowed and became shallower under drought stress. The inflection points near 1390 and 1500 nm were most sensitive to drought stress. Differences between drought stress and control swards were detected shortly before leaf water content dropped below 80%. The evolution of inflection point wavelength positions reversed under drought stress, except for the inflection point at the red edge where the shift to longer wavelengths during growth accelerated. The relation between inflection points at 705 and 1390 nm differentiated unstressed swards at an early growth stage from drought-stressed swards in a later growth stage
    Imaging spectroscopy for early detection of nitrogen deficiency in grass swards
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2003
    NJAS Wageningen Journal of Life Sciences 51 (2003)3. - ISSN 1573-5214 - p. 297 - 317.
    grasveld - lolium perenne - mineraaltekorten - stikstof - spectroscopie - stress - reflectiefactor - grass sward - lolium perenne - mineral deficiencies - nitrogen - spectroscopy - stress - reflectance - red edge - canopy reflectance - thylakoid proteins - leaf reflectance - corn leaves - chlorophyll - carotenoids - spectra - growth - plants
    The potential of an experimental imaging spectroscopy system with high spatial (0.16–0.28 mm²) ) and spectral resolution (5–13 nm) was explored for early detection of nitrogen (N) stress. From June through October 2000, a greenhouse experiment was conducted with 15 Lolium perenne L. mini-swards and 5 N treatments. Images were recorded twice a week. With the experimental system, spectra of grass leaves in the canopy can be obtained. Treatment effects on ground cover (GC) and changes in leaf spectral characteristics were studied separately. Leaf pixels with similar reflection intensity were grouped in intensity classes (IC). An index of reflection intensity (IRI) indicates the percentages of strongly reflecting grass pixels. Blue edge, green edge and red edge positions were calculated for each IC. Both GC and IRI increased until harvest, with largest increases for liberal N treatments. The width of the chlorophylldominated absorption band around 680 nm (CAW) increased up to a maximum of 133 nm for both liberal and limited N in the first two weeks after harvesting. CAW decreased for limited N in the second half of the growth period in contrast to liberal N. At harvest CAW explained 95% of the variation in relative dry matter (DM) yield between treatments. Principal component analyses showed an intertwined response of the principal components to both DM yield and N content. Edge positions changed strongly with IC. Possible effects of sensor characteristics, canopy geometry, leaf angle and changes in leaf characteristics with canopy position on the observed relation between IC and edge position are discussed.
    Landbouw en zorg in de provincie. Inventarisatie van provinciaal beleid landbouw en zorg
    Elings, M. ; Hassink, J. ; Ketelaars, T.J.W.M. - \ 2003
    Wageningen : Plant Research International (Rapport / Plant Research International 63) - 54
    landbouwbeleid - gezondheidsbeleid - sociaal beleid - regionaal beleid - inventarisaties - nederland - provincies - zorgboerderijen - agricultural policy - health policy - social policy - regional policy - inventories - netherlands - provinces - social care farms
    Om zicht te krijgen op de verschillende beleidsplannen en stimuleringsregelingen van de provincies en om een indruk te krijgen van het resultaat van die beleidsmatige activiteiten, is een inventarisatie uitgevoerd van de beleidsactiviteiten van alle provincies in Nederland. Per hoofdstuk worden de provincies besproken. In het laatste hoofdstuk worden knelpunten besproken waar meerdere provincies tegen aan lopen en worden modellen en fasen van beleidsontwikkeling beschreven
    Imaging spectroscopy for characterisation of grass swards
    Schut, A.G.T. - \ 2003
    Wageningen University. Promotor(en): J. Goudriaan, co-promotor(en): Jan Ketelaars. - [S.I.] : S.n. - ISBN 9789058088376 - 264
    grasveld - graslanden - spectroscopie - spectrometrie - remote sensing - reflectie - reflectiefactor - detectie - groei - stress - lolium perenne - trifolium repens - graslandbeheer - lolium perenne - trifolium repens - grass sward - grasslands - grassland management - spectroscopy - spectrometry - remote sensing - reflection - reflectance - detection - growth - stress

    Keywords: Imaging spectroscopy, imaging spectrometry, remote sensing, reflection, reflectance, grass sward, white clover, recognition, characterisation, ground cover, growth monitoring, stress detection, heterogeneity quantification

    The potential of imaging spectroscopy as a tool for characterisation of grass swards was explored with respect to growth monitoring, detection of nitrogen and drought stress, and assessment of dry matter yield, clover content, nutrient content, feeding value, sward heterogeneity and production capacity. To this end, an experimental imaging spectroscopy system was developed. The system detects reflection in image lines in the wavelength range from 405-1659 nm with three different sensors at 1.3 m above the soil surface. Spectral resolution varies between 5-13 nm, and spatial resolution between 0.28-1.45 mm 2per pixel at the soil. As a result of system design, reflection intensity is a function of leaf height and leaf angle. The system was tested on mini swards grown in containers. For each mini sward, 42 image lines were recorded in a regular sampling pattern per recording event.

    Five experiments were conducted with Lolium perenne L. and/or Trifolium repens L. mini swards. In these experiments degree of sward damage, level of nitrogen (N) application (two experiments), water supply and white clover content were varied. In the sward damage experiment and in one N experiment light interception was recorded regularly; at harvest, also crop height and canopy reflectance (with a Cropscan) was measured. Mini swards were harvested at a fixed level and in one of the N experiments in three strata. During the experiments, hyperspectral reflectance was recorded 2-4 times per week.

    Image lines were classified to separate pixels containing soil, dead material and green leaves. These classes were subdivided into reflection intensity classes. Ground cover (GC), reflection intensity, image line texture, spatial heterogeneity and patterns, and spectral characteristics of green leaves were quantified. An index of reflection intensity (IRI) measured the distribution of green pixels over intensity classes and quantified vertical canopy geometry. Horizontal sward heterogeneity was quantified with the spatial standard deviation of GC (GC-SSD) and logarithmically transformed GC (TGC-SSD), and image line texture and spatial patterns with wavelet entropy (WE). Spectral characteristics were quantified with shifts of various spectral edges. Partial least squares (PLS) models combining spectral and spatial information were calibrated and validated on two separate data-sets from the sward damage and one N experiment, in order to predict dry matter (DM) yield, feeding quality and nutrient content. Effects of replicate observations on reduction of prediction error were studied for different fractions of model bias.

    GC was differently related to light interception under a cloudy sky and under a clear sky (R 2adj = 0.87-0.94) and also for dense and open swards. Growth was accurately monitored with evolution of GC and IRI, and GC and IRI at harvest were strongly related to DM yield (R 2adj = 0.75-0.82). Seasonal means of GC and IRI were strongly (R 2adj = 0.77-0.93) related to annual DM matter yield and light interception capacity. There was a clear (R 2adj = 0.69) relation between seasonal mean GC-SSD and tiller density. Seasonal means of GC-SSD differentiated dense from damaged swards. The WE of image line texture robustly differentiated clover from grass swards, while mixtures had intermediate values. Position of spectral edges was strongly related to reflection intensity. This relation differed for grass and clover swards, varied with N supply level and changed after harvesting canopy strata. Leaf angle was identified as the most important factor affecting this relationship. Drought stress was detected in an early stage, when DM content of leaves was still below 20%, from shifts of edges near water absorption features. A combination of shifts of the green and red edge was strongly related (R 2=0.95) to DM yield reduction due to N shortage. The prediction errors relative to the mean (of validation sets) of the PLS models were 6.2-11.7 % for N content, 5.5-9.1 % for DM content, 13.6-18.7 % for sugar content, 6.0-7.5 % for ash content, and 3.5-4.8 % for crude fibre content. Predictions of P, K, S, Mg, Na and Fe were robust in both experiments. Combining GC and IRI with mean sward spectra resulted in a prediction error of 235-268 kg DM ha -1for yields of less than 1000 up to 4000 kg DM ha -1. Multiple observations may reduce the mean prediction error for DM yield with 27 to 54%, depending on model bias and number of observations. The accuracy of DM yield assessment with imaging spectroscopy was better than with the disk plate meter or Cropscan. It is concluded that imaging spectroscopy is a powerful tool in grassland research and may provide valuable information for fine-tuning of grassland management. In this study it provided fast, automatic and non-destructive means for monitoring and quantification of growth, and estimating dry matter yield, spatial heterogeneity and sward damage, nitrogen and water deficiency, clover content, feeding quality and nutrient content of swards. Finally, system requirements for application of imaging spectroscopy in the field are discussed.

    Macular pigment density in relation to serum and adipose tissue concentrations of lutein and serum concentrations of zeaxanthin
    Broekmans, W. ; Berendschot, T.T.J.M. ; Klopping-Ketelaars, I.A.A. ; Vries, A.J. de; Goldbohm, R.A. ; Tijburg, L.B.M. ; Kardinaal, A.F.M. ; Poppel, G. van - \ 2002
    American Journal of Clinical Nutrition 76 (2002)3. - ISSN 0002-9165 - p. 595 - 603.
    age-related maculopathy - plasma carotenoid concentrations - nutrition examination survey - optical-density - menstrual-cycle - national-health - iris color - vitamin-a - degeneration - dietary
    Background: Macular pigment (MP), concentrated in the central area of the retina, contains the carotenoids lutein and zeaxanthin. A low MP density could be a risk factor for age-related macular degeneration. Little information is available regarding MP density in relation to serum lutein and zeaxanthin and adipose lutein concentrations in a general population. Objective: The objective was to investigate the associations between MP density and serum lutein, serum zeaxanthin, and adipose lutein, taking into account potential confounders in a population. Design: Volunteers (n = 376) aged 18¿75 y were recruited. In a cross-sectional design, serum (n = 376) and adipose tissue (n = 187) were analyzed for carotenoids, and MP density was measured by spectral fundus reflectance. Results: Mean MP density in the total study group was 0.33 ± 0.15. MP density was 13% higher in men than in women (P <0.05). Serum and blood concentrations of -tocopherol, vitamin C, and all carotenoids except lycopene were significantly higher in women. Adipose lutein concentrations were also significantly higher in women than in men. Regression models showed a positive significant association between MP density and serum lutein, serum zeaxanthin, and adipose lutein concentrations in men after adjustment for age, but no relation in women. In men, serum lutein remained significantly associated with MP density after adjustment for age, total cholesterol, body mass index, and smoking. Conclusion: The associations between MP density and serum lutein, serum zeaxanthin, and adipose lutein concentrations are stronger in men than in women
    Lens aging in relation to nutritional determinants and possible risk factors for age-related cataract
    Berendschot, T.T.J.M. ; Broekmans, W. ; Klopping-Ketelaars, I.A.A. ; Kardinaal, A.F.M. ; Poppel, G. van; Norren, D. van - \ 2002
    Archives of Ophthalmology 120 (2002)12. - ISSN 0003-9950 - p. 1732 - 1737.
    beaver dam eye - macular pigment density - human crystalline lens - body-mass index - cigarette-smoking - optical-density - vitamin-c - antioxidant vitamins - nuclear opacities - serum carotenoids
    Objective To investigate whether nutritional factors and possible risk factors for cataract influence the lens optical density (LOD). Design Three hundred seventy-six subjects, aged 18 to 75 years, were recruited. In a cross-sectional design, serum was analyzed for lutein, zeaxanthin, vitamin C, -tocopherol, and cholesterol levels. Adipose tissue (n = 187) was analyzed for lutein level. The LOD and the macular pigment optical density (MPOD) were measured by spectral fundus reflectance. Results The mean ± SD LOD at 420 nm was 0.52 ± 0.17. It showed a significant association with age ( = .008, P
    Novel Imaging Spectroscopy for Grass Sward Characterization
    Schut, A.G.T. ; Ketelaars, J.J.M.H. ; Meuleman, J. ; Kornet, J.G. ; Lokhorst, C. - \ 2002
    Biosystems Engineering 82 (2002)2. - ISSN 1537-5110 - p. 131 - 141.
    corn leaves - reflectance - nitrogen - leaf - chemistry - images
    Attempts to improve grassland management may benefit from the use of new sensing techniques, such as imaging spectroscopy. In order to explore the potential of hyperspectral imaging spectroscopy for rapid and objective characterization of grass swards an experimental prototype has been developed. From a height of 1 m, the system detects reflections at high spatial (0.16-1-45 mm(2)) and high spectral resolutions (5-17nm) at wavelengths between 405 and 1659nm. Detailed information is provided on design, characteristics and test results. Results show that reflection intensity is related to height position in the sward and leaf angle. Grass leaves were recognized accurately. Images of a sports field and a production sward with similar ground cover fractions could be easily distinguished. With the described system, canopy structure can be characterized by ground cover, the distribution of reflection intensity and image texture. Spectral characteristics can be obtained at leaf level. (C) 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved
    'Krapper bemesten dankzij benutten mineralisatie'
    Anonymous, - \ 2002
    Oogst : weekblad voor de agrarische ondernemer. Landbouw 15 (2002)13. - ISSN 1566-2616 - p. 53 - 53.
    veehouderij - varkenshouderij - zeugen - diervoeding - voeropname - onbeperkte voedering - groepshuisvesting - livestock farming - pig farming - sows - animal nutrition - feed intake - unrestricted feeding - group housing
    Groepshuisvesting van zeugen en onbeperkt voeren door een uitgekiende voersamenstelling levert alleen maar voordelen op volgens veehouder Ketelaars
    Landbouw en zorg in beeld : blik op heden en toekomst
    Ketelaars, D. ; Erp, N. ; Hassink, J. - \ 2002
    Wageningen : Plant Research International - 32
    landbouw - landbouwbedrijven - sociologie - sociale zorg - zorgboerderijen - schoolboerderijen - agriculture - farms - sociology - social care - social care farms - school farms
    Verkenning van de uitstraling van een mineralenproject
    Ketelaars, D. ; Leeuwis, C. - \ 2002
    Wageningen : Agro Management Tools (Rapport project klimop 6) - 27
    mineralen - melkveehouderij - agrarische bedrijfsvoering - karteringen - kennis - dierhouderij - minerals - dairy farming - farm management - surveys - knowledge - animal husbandry
    FoodPrint : systematiek voor de inrichting van traceringssystemen : benut de meerwaarde van tracking & tracing
    Ketelaars, N.J.J.P. ; Verdenius, F. ; Top, J.L. - \ 2002
    Voedingsmiddelentechnologie 35 (2002)13. - ISSN 0042-7934 - p. 30 - 33.
    Imaging spectroscopy for detection of drought stress
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2001
    In: Third European Conference on Precision Agriculture : Third European Conference of the European Federation for Information Technology in Agriculture, Food and the Environment, Montpellier 2001. - [S.l.] : [s.n.], 2001 - p. 65 - 65.
    Imaging spectroscopy for detection of nitrogen stress
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2001
    In: Third European Conference on Precision Agriculture : Third European Conference of the European Federation for Information Technology in Agriculture, Food and the Environment, Montpellier 2001. - [S.l.] : [s.n.], 2001 - p. 64 - 64.
    Fruits and vegetables and cardiovascular risk profile: a diet controlled intervention study
    Broekmans, W.M.R. ; Klopping-Ketelaars, W.A. ; Klurft, C. ; Berg, H. van den; Kok, F.J. ; Poppel, G. van - \ 2001
    European Journal of Clinical Nutrition 55 (2001). - ISSN 0954-3007 - p. 636 - 642.
    Interventions: During 4 weeks 24 volunteers consumed a standardised meal, consisting of 500 g/day fruit and vegetables and 200 ml/day fruit juice ('high' group) and 23 volunteers consumed 100 g/day fruit and vegetables ('low' group) with an energy and fat controlled diet. Results: Final total cholesterol was 0.2 (95I-0.5-0.03) mmol/l lower in the high group than in the low group (P>0.05). Final fibrinogen and systolic blood pressure were 0.1 (-0.1-0.4) g/l and 2.8 (-2.6-8.1) mmHg higher in the high group than in the low group (P>0.05), respectively. Also, other final serum lipid concentrations, diastolic blood pressure and other haemostatic factors did not differ between both groups. Conclusions: This was a small randomised well-controlled dietary intervention trial of short duration with a considerable contrast in fruit and vegetable consumption. No effects on serum lipids, blood pressure and haemostatic variables were observed.
    Effects of nitrogen stress in grass swards on evolution of ground cover and spectral characteristics of leaf strata
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2001
    Toulouse, France : Unknown Publisher (Remote Sensing for Agriculture, Ecosystems, and Hydrology III. )
    Effects of nitrogen stress in grass swards on evolution of ground cover and spectral characteristics of leaf strata
    Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2001
    In: Remote sensing for agriculture, ecosystems, and hydrology III : 8th International Symposium on remote sensing 2001, Toulouse, France / M. Owe and G. D'Urso. - [S.l.] : [s.n.], 2001 - p. 191 - 198.
    Stikstofvervluchtiging uit mest: berekening op basis van mineralenbalansen
    Bruins, W.J. ; Dijksterhuis, G.H. ; Velthof, G.L. ; Ketelaars, J.J.M.H. - \ 2000
    Wageningen : Plant Research International - 16
    vervluchtiging - dierlijke meststoffen - ammoniak - stikstof - emissie - boekhouding - stikstofmeststoffen - landbouw - mest - milieu - nutriënten - veehouderij - volatilization - animal manures - ammonia - nitrogen - emission - accounting - nitrogen fertilizers
    Imaging spectroscopy for characterization of spatially heterogeneous canopies
    Schut, A.G.T. ; Ketelaars, J.J.M.H. ; Meuleman, J. ; Kornet, J.G. ; Lokhorst, C. - \ 2000
    In: Progress of agricultural information technology / Zhao, C., - p. 288 - 293.
    Imaging spectroscopy for characterization of spatially heterogenous canopies
    Schut, A.G.T. ; Ketelaars, J.J.M.H. ; Meuleman, J. ; Kornet, J.G. ; Lokhorst, C. - \ 2000
    In: Proceedings ISIAIT (International Symposium Intelligent Agricultural Information Technology), 1-4 December, China, 6 pp
    Fruits and vegetables increase plasma carotenoids and vitamins and decrease homocysteine in humans
    Broekmans, W.M.R. ; Klöpping-Ketelaars, I.A.A. ; Schuurman, R.R.W.C. ; Verhagen, H. ; Berg, H. van den; Kok, F.J. ; Poppel, G. van - \ 2000
    The Journal of Nutrition 130 (2000)6. - ISSN 0022-3166 - p. 1578 - 1583.
    Observational epidemiologic studies have shown that a high consumption of fruits and vegetables is associated with a decreased risk of chronic diseases. Little is known about the bioavailability of constituents from vegetables and fruits and the effect of these constituents on markers for disease risk. Currently, the recommendation is to increase intake of a mix of fruits and vegetables ("five a day"). We investigated the effect of this recommendation on plasma carotenoids, vitamins and homocysteine concentrations in a 4-wk dietary controlled, parallel intervention study. Male and female volunteers (n = 47) were allocated randomly to either a daily 500-g fruit and vegetable ("high") diet or a 100-g fruit and vegetable ("low") diet. Analyzed total carotenoid, vitamin C and folate concentrations of the daily high diet were 13.3 mg, 173 mg and 228.1 ?g, respectively. The daily low diet contained 2.9 mg carotenoids, 65 mg vitamin C and 131.1 ?g folate. Differences in final plasma levels between the high and low group were as follows: lutein, 46$95␌onfidence interval (CI) 28–64]; ß-cryptoxanthin, 128ø98–159); lycopene, 22ø8–37); -carotene, 121ø94–149); ß-carotene, 45ø28–62); and vitamin C, 64ø51–77) (P < 0.05). The high group had an 11ø-18 to -4) lower final plasma homocysteine and a 15ø0.8–30) higher plasma folate concentration compared with the low group (P < 0.05). This is the first trial to show that a mix of fruits and vegetables, with a moderate folate content, decreases plasma homocysteine concentrations in humans.
    Ammoniakemissie op De Marke: overzicht en perspectieven : samenbundeling rapporten van themadag "Van voer tot ammoniak"
    Schans, F. van der; Hilhorst, G.J. ; Middelkoop, N. ; Biewinga, E. ; Putten, T. van der; Ketelaars, J. - \ 1999
    Hengelo : De Marke (Rapport / De Marke no. 24)
    ammoniak - emissie - vervluchtiging - melkveehouderij - melkvee - luchtverontreiniging - dierlijke meststoffen - nederland - ammonia - emission - volatilization - dairy farming - dairy cattle - air pollution - animal manures - netherlands
    Bio-raffinage van gras
    Ketelaars, J.J.M.H. - \ 1999
    In: Jaarverslag 1998 Wageningen : AB-DLO - p. 42 - 44.
    Modélisation des effets d'une supplémentation alimentaire u base de protéines
    Ketelaars, J.J.M.H. ; Kané, M. - \ 1998
    In: L'intensification agricole au Sahel / Breman, H., Sissoko, K., Paris : Karthala - p. 401 - 427.
    Perspectives for improving efficiency of nutrient use in livestock production in The Netherlands
    Ketelaars, J.J.M.H. ; Meer, H.G. van der - \ 1998
    In: Proceedings of an International Workshop on Environmentally Friendly Management of Farm Animal Waste, November 25-29, 1997, Sapporo, Japan / Matsunaka, T., - p. 159 - 164.
    Searching behaviour of entomopathogenic nematodes : roots and soil temperature determine success of black vine weevil (Otiorhynchus sulcatus) control
    Tol, R.W.H.M. van; Bezooijen, J. van; Ketelaars, T.A.C.M. - \ 1998
    International Organisation of biological Control Bulletin 21 (1998)4. - p. 187 - 191.
    La supplementation du betail: une necessite!
    Kaasschieter, G.A. ; Coulibaly, Y. ; Heitkonig, I.M.A. ; Ketelaars, J.J.M.H. - \ 1998
    In: L'intensification Agricole au Sahel / Breman, H., Sissoko, K., - p. 79 - 105.
    Lotz, L.A.P. ; Veen, J.A. van; Kropff, M.J. - \ 1998
    In: Ontwerpen voor een schone landbouw : achtergrondstudie voor de verkenning hulpstoffen en energie in landbouwsystemen in 2015 / Ketelaars, J.J.M.H., de Ruiter, F.J., Den Haag : NRLO (NRLO-rapport ) - ISBN 9789050590228 - p. 35 - 58.
    Parasitaire nematoden
    Zoon, F.C. - \ 1997
    In: Ontwerpen voor een schone landbouw / Ketelaars, J.J.M.H., de Ruiter, F.J., - p. 44 - 47.
    Effects of floor design and floor cleaning on ammonia emission from cubicle houses for dairy cows
    Braam, C.R. ; Ketelaars, J.J.M.H. ; Smits, M.C.J. - \ 1997
    Netherlands Journal of Agricultural Science 45 (1997). - ISSN 0028-2928 - p. 49 - 64.
    The traditional slatted floor was compared with 2 different solid floor systems: a non-sloped (L) and a 3% one-sided sloped floor (S), combined with a highly frequent (96 times/day) or normal (12 times/day) removal of manure by a scraper. NH3 emissions were measured continuously over 2 separate 2-week periods between 14 March and 4 July 1995. Urease activity on the solid floors was measured as the accumulation of ammoniacal N in a urea solution in contact with the floor surface, expressed as g NH3/msuperscript 2 per h. NH3 emission from L12 was similar to that from the compartment with a slatted floor but S12 decreased NH3 emission by 21%. Increasing the scraping frequency from 12 to 96 times/day decreased NH3 emission (by 5 and 26% in L96 and S96, respectively). During the last testing period, just before removal of the cows, NH3 emission from the compartment with the S12 variant was 30-35 g NH3/h (10 cows). After removal of the cows this level decreased to 3-17 g NH3/h (average: 8.7 g NH3/h). Covering the openings through which the slurry collected by the scraper system was dropped in the pit, reduced emission to 4-10 g NH3/h (average: 5.5 g NH3/h). However, covering only decreased NH3 emission when the inside temperature was higher that outside. Urease activity at\\less than or =\\10 and approximately 20 degrees C was 0 and 0.04 g NH3/msuperscript 2 per h, respectively. Up to a urease activity of about 2 g NH3/msuperscript 2 per h, NH3 emission increased with increasing urease activity. At higher levels of urease activity the amount of urea on the floor surface or the rate of volatilization of NH3 from a urine puddle or from the slurry pit to the inside air limited the NH3 emission. It is concluded that the slope of the floor had more impact on reducing ammonia emission than increasing the scraping frequency. Solid floors without a slope may not decrease ammonia emission compared with slatted floors
    Effects on intake of supplementing low-quality roughage with protein-rich feeds
    Ketelaars, J.J.M.H. ; Kaasschieter, G.A. ; Kané, M. - \ 1997
    In: Poster abstract, International Grassland Congress 1997 (1182)
    Ontwerpen voor een schone landbouw. Achtergrondstudie voor de verkenning hulpstoffen en energie in landbouwsystemen in 2015
    Ketelaars, J.J.M.H. ; Ruijter, F.J. de - \ 1997
    Unknown Publisher - 107 p.
    Environmental implications of grass and forage based systems of milk production
    Meer, H.G. van der; Ketelaars, J.J.M.H. ; Aarts, H.F.M. - \ 1997
    In: Grass is greener?
    Effecten van verlaging van de stikstofuitscheiding per dier op de nutriëntenbalansen en -emissies vanbedrijven en regio's
    Meer, H.G. van der; Ketelaars, J.J.M.H. ; Putten, A.H.J. van der - \ 1997
    In: Workshop: Betekenis van N-benutting door landbouwdieren voor deN-kringloop/N-balans op veehouderijbedrijven, 11 juni 1997. ID-DLO rapport 97.018 - p. 24 - 30.
    Effect of cell walls, dry matter and protein supply on endogenous nitrogen flow in the small intestine of sheep.
    Lammers-Wienhoven, S.C.W. ; Voigt, J. ; Ram, L. ; Bruchem, J. van; Ketelaars, J. ; Tamminga, S. - \ 1997
    Journal of Animal Physiology and Animal Nutrition 78 (1997). - ISSN 0931-2439 - p. 129 - 140.
    Practical use of entomopathogenic nematodes in nursery stock: economic and biological aspects of vine weevil (Otiorhynchus sulcatus) control.
    Tol, R.W.H.M. van; Bezooijen, J. van; Ketelaars, D.A.C.M. - \ 1997
    In: Proceedings IOBC workshop, Denmark (1997) 6 pp
    Secretion and reabsorption of endogenous protein along the small intestine of sheep: estimates derived from 15N dilution of plasma non-protein-N.
    Bruchem, J. van; Voigt, J. ; Lammers-Wienhoven, S.C.W. ; Schönhusen, U. ; Ketelaars, J.J.M.H. ; Tamminga, S. - \ 1997
    The British journal of nutrition 77 (1997)2. - ISSN 0007-1145 - p. 273 - 286.
    Herintroductie van graslandplanten
    Geerts, R.H.E.M. ; Ketelaars, J.J.M.H. ; Oomes, M.J.M. ; Korevaar, H. ; Werf, A. van der - \ 1996
    In: Jaarverslag 1995 Wageningen/Haren : AB-DLO - p. 65 - 68.
    Oxygen efficiency and the control of energy flow in animals and humans
    Ketelaars, J.J.M.H. ; Tolkamp, B.J. - \ 1996
    Journal of Animal Science 74 (1996)12. - ISSN 0021-8812 - p. 3036 - 3051.
    A new theory of feed intake regulation in ruminants has been developed as an alternative to the traditional view that feed consumption is limited by the physical and physiological constraints of the animal. Historical evidence that supports the traditional view has been examined. The new theory is based on the assumption that feed consumption has both positive and negative outcomes (benefits and costs). In a non-reproducing animal, benefits include yield of net energy for maintenance and gain. Costs are represented by the total oxygen consumption of the animal. The ratio between benefits and costs is calculated as the oxygen efficiency of feeding behavior, i.e., yield of net energy per liter of oxygen consumed. Voluntary energy intake corresponds to the feed consumption level at which oxygen efficiency is maximum. Literature examples were used to illustrate the predictive power of this theory. Differences in intake can be related to the efficiency of energy utilization, i.e., the animals' cost of processing feed. Current knowledge of the nature and causes of variation in processing costs is summarized. Secretory and absorptive processes associated with fiber consumption may explain why fiber can alter feed intake. Maximizing oxygen efficiency seems to be a unifying principle controlling other types of behavior such as locomotory behavior in humans. Possible physiological mechanisms controlling self-selected rates of locomotion are discussed in relation to the control of energy flow in ruminants.
    A technical coefficient generator for land use activities in the Koutiala region of South Mali
    Hengsdijk, H. ; Quak, W. ; Bakker, E.J. ; Ketelaars, J.J.M.H. - \ 1996
    Wageningen : AB-DLO [etc.] - ISBN 9789073384484 - 96
    landgebruik - sahel - mali - agro-ecologie - land use - agroecology
    Description quantitative des systOmes de production animale en zone Soudano-Sahélienne
    Bakker, E.J. ; Hengsdijk, H. ; Ketelaars, J.J.M.H. - \ 1996
    Wageningen : AB-DLO [etc.] - 36
    productiviteit - rentabiliteit - dierhouderij - sudan - sahel - productivity - profitability - animal husbandry - sudan - sahel
    PROGRESS, PROteins from GRass Extraction SystemS
    Rutgers, B. ; Ketelaars, J.J.M.H. ; Hoogerbrugge, A. - \ 1996
    Unknown Publisher - 41 p.
    Reorientational properties of fluorescent analogues of the protein kinase C cofactors diacylglycerol and phorbol ester.
    Pap, E.H.W. ; Ketelaars, M. ; Borst, J.W. ; Hoek, A. van; Visser, A.J.W.G. - \ 1996
    Biophysical Chemistry 58 (1996). - ISSN 0301-4622 - p. 255 - 266.
    The reorientational properties of the fluorescently labelled protein kinase C (PKC) cofactors diacylglycerol (DG) and phorbol ester (PMA) in vesicles and mixed micelles have been investigated using time-resolved polarised fluorescence. The sn-2 acyl chain of DG was replaced by diphenylhexatriene- (DPH) propionic acid, while a dansyl labelled analogue of phorbol ester was used. The extent of ordering of DPH-DG in vesicles turned out to be slightly different from that of the control choline lipid DPH-PC. Addition of PKC to vesicles containing 30 mole% brain PS considerably slowed down the DPH-DG anisotropy decay. This was not observed when DPH-DG was replaced by DPH-PC. Analysis of the fluorescence anisotropy decays of these DPH-lipids in micelles polyoxyethylene-9-laurylether mixed with 10 mole% of the essential phosphatidylserine allowed estimation of their lateral diffusion, orientation distribution and reorientational dynamics within the micelles. Addition of PKC resulted in a significantly slower decay of the fluorescence anisotropy of both DPH-DG and DPH-PC even in the absence of calcium, indicating a calcium independent complexation of PKC with the PS containing micelles, Addition of calcium resulted in a further reduction of the decay of anisotropy of DPH-DG but not of DPH-PC indicating that the Ca2 dependent immobilisation is cofactor-specific. Similar specific interactions with PKC resulted in a slower decay of dansylated PMA when calcium and PS were present.
    Nuclear magnetic resonance study of the conformation and dynamics of ß-casein at the oil/water interface in emulsions.
    Beek, L. ter; Ketelaars, M. ; McCain, D.C. ; Smulders, P.E.A. ; Walstra, P. ; Hemminga, M.A. - \ 1996
    Biophysical Journal 70 (1996). - ISSN 0006-3495 - p. 2396 - 2402.
    VervIuchtiging van ammoniak uit de rundveehouderij
    Ketelaars, J.J.M.H. ; Putten, A.J.H. van der; Ven, G.W.J. van de; Aarts, H.F.M. - \ 1995
    In: AB-DLO Jaarverslag 1994 - p. 46 - 49.
    Effect van celwanden op de produktie en terugresorptie van endogeen eiwit in de dunne darm bij schapen.
    Lammers-Wienhoven, T. ; Ram, L. ; Philipse, B. ; Voigt, J. ; Bruchem, J. van; Ketelaars, J. ; Tamminga, S. - \ 1994
    In: Verslag 19e Studiedag Nederlandstalige Voedingsonderzoekers, Wageningen - p. 29 - 30.
    Flow of endogenous protein along the small intestine of sheep - Effect of cell walls.
    Voigt, J. ; Bruchem, J. van; Lammers-Wienhoven, T. ; Ketelaars, J.J.M.H. ; Tamminga, S. - \ 1994
    Proceedings of the society of nutritional physiology 3 (1994). - p. 104 - 104.
    The effect of parasitism on nutrient metabolism and productivity in small ruminants
    Akinbamijo, O.O. - \ 1994
    Agricultural University. Promotor(en): D. Zwart; T. Wensing. - S.l. : S.n. - ISBN 9789054852957 - 145
    diergeneeskunde - herkauwers - parasitosen - parasieten - trypanosomiase - voer - voedingswaarde - diervoeding - veterinary science - ruminants - parasitoses - parasites - trypanosomiasis - feeds - nutritive value - animal nutrition

    The investigation of voluntary feed intake (VFI) and nitrogen retention (NRET) during parasitic infections in small ruminants is the central theme of this thesis. An attempt was made to examine the effects of trypanosomiasis on feed intake, digestibility, nitrogen retention and animal products. In addition, a similar investigation was conducted during a low to medium level fascioliasis infection in Menz sheep. The relationship between digestible organic matter intake (DOMI) rectal temperature (RT) and maintenance requirements was also studied in healthy goats.

    The infected subjects manifested an aggregate of some distinct but not mutually exclusive responses. These include anorexia, fever, increased metabolic rate, lowered nitrogen retention and reduced animal productivity characterized by the host's poor growth rate and weight loss. Although the feed intake appears to be a major factor in the disease process, the observed derangements in productivity and physiological response to parasitic infection could not be fully explained by anorexia. Therefore, it seems that survival and the productive performance of infected animals depended on the adaptive measures they are able to employ to meet nitrogen and energy requirements during the periods of insufficient nutrient supply or inefficient feed utilization.


    A depression in feed intake is a common feature in infected subjects, although the mechanisms involved remain unclear. Infection-induced anorexia is a major factor limiting the availability of energy for maintenance and production in parasitized hosts. This phenomenon has been widely reported in both human and animal subjects as one of the earliest signs of a patent infection (Ilemobade and Balogun, 1981; Symons, 1985; Keusch and Farthing, 1986; Holmes, 1987; Akinbamijo, 1988; Verstegen et al 1991; Zwart et al , 1991). Anorexia is an important aspect of parasitic infections, but studies using pair-feeding techniques have demonstrated that infected animals also show reduced feed utilization and energy retention relative to their parasite-free counterparts on the same level of feed intake (Sykes and Coop, 1976; Coop et al , 1982).

    The onset of infection is characterized by the acute phase response during which anorexia, wasting of body tissues and changes in metabolism of carbohydrates, lipids and proteins occur (Baracos et al , 1987). Fever, a major factor in energy metabolism, is a conventional occurrence in haemo-protozoan infections such as trypanosomiasis (Holmes, 1987; Akker, 1988; Zwart et al , 1991; Verstegen et al , 1991) and malaria (Cohen and Lambert, 1982). This rise in body temperature implies an elevation of heat production caused by increased metabolic rates. Lower nitrogen retention has been reported in infected human and animal subjects during most nutrition-infection interactions (Beisel et al , 1987; Dargie et al , 1979; Morris, 1988). The reduced nitrogen balance observed in parasitized hosts is not only a consequence of the reduced feed intake (Symons, 1985): fever and the related increases in tissue catabolism (Baracos et al , 1987), intestinal and renal protein losses (Ingh et al , 1976; Holmes, 1987), high urea and total proteins concentrations in the serum (Finco, 1989) and high urinary nitrogen excretion (Roseby, 1977; Akinbamijo, 1988) have all been implicated during parasitism.

    The increased catabolism of proteins during the acute infection is reflected in the increased urea production and nitrogen excretion often seen in infected animals (Finco, 1989). These wasting events, culminating in lower/negative nitrogen retention reduce the productivity of infected animals.

    During parasitic infections in which anorexia and fever occur concomitantly, lipolysis and ketogenesis are common features (Keusch, 1984). After the glycogen reserve has been exhausted, during the first few hours of anorexia, the fat depot is used as an interim measure to meet the body's energy requirements. High concentrations of free fatty acids and ketone bodies in body fluids are an indication of lipolysis and partly oxidation of lipids. They are at a later phase accompanied by protein mobilization, reflected in increased urea in the urine.

    The energy deficit during infection boosts the rate of energy needs. Hence, the changes in the composition of the serum often observed during infection-induced anorexia are a reflection of the subnormal caloric intake (Blackburn et al , 1991; Keusch, 1984; Bruss, 1989). These physiological changes occurring in concert, with complementary effects on each other, result in a serious negative energy balance, accompanied by a cumulative depletion of body energy stores, precipitating a lowered or negative energy and nitrogen balances (Clowes et al , 1976; Beisel, 1985; Keusch and Farthing, 1986; Baracos et al , 1987; Blaxter, 1989).


    In view of their pathogenesis, it is often assumed that endo-parasitism must be associated with changes in the gastro-intestinal function (Holmes, 1987). However, parasitic infections do not normally seem to affect the digestive and/or absorptive capacity of the host, even when infection rates are high (Parkins et al , 1973; Roseby, 1977; Reveron and Topps, 1970; Reveron et al , 1974). Similar findings have been reported in sheep infected with Fasciola hepatica (Hawkins and Morris, 1978) and in calves infected with lungworms (Verstegen et al , 1989). Holmes (1987) suggested that the digestion and absorption of amino-acids might decrease as a result of endogenous protein draining into the gut of parasitized animals, but this is not a usual event in helminthiasis. In general, it is not impaired digestion and absorption but rather the increased metabolic demands on the hosts that are the important causes of the low productivity of parasitized hosts (Baracos et al , 1987).


    The net effect of infection on productivity is mediated primarily via a reduction in the energy available for productive purposes. Thus, changes in live body weight are a common yardstick for judging the effects of parasitism on animal productivity. It is generally acknowledged that diseased animals lose or gain weight more slowly than their non-infected counterparts. The low weight gains and differences in the productive capacity in bovine (Schillhorn van Veen, 1974; Kroonen et al , 1986) and ovine (Roseby, 1970; Hawkins and Morris, 1978; Tekelye et al , 1992 a&b) infections are primarily due to reduced voluntary feed intake. In addition to changes in the body weight, alterations in body composition do occur and this can have major implications for productivity. It is well established that under nutrition can cause changes in body composition of healthy red deer (Wolkers, 1993). In sheep, parasitic infection is found to have the same effects (Sykes and Coop, 1976, 1977).

    The shortfall in energy required for productivity has a direct quantitative effect on animal products during infection. It has been demonstrated that milk yield and composition are affected during infection with trichostrongylosis (Bliss and Todd, 1976; 1977) and fascioliasis (Randell and Bradley, 1980). Both the quality and the quantity of wool have also been reported to be affected by infection (Bliss and Todd, 1977; Barger and Gibbs, 1981; Leyva et al , 1982).

    Reproductive disorders in male and female humans and animals caused by Trypanosoma infection are widely reported in the literature (Ikede et al, 1988; Akpavie et al , 1987). The effects of infection have been demonstrated on conception rates and pregnancy in cattle (Ogwu and Nuru, 1981; Ogwu et al , 1986; Oakley et al , 1979) and sheep (Reynolds and Ekwuruke, 1988) leading to a lower reproductive index (RI) (Gabina, 1988).

    Many of the major parasitic diseases such as trypanosomiasis, babesiosis, malaria and fascioliasis are characterized by anaemia. The decline in packed cell volume (PCV) during parasitic infections is often a confirmation that a disease process has set in. The aetiology of parasite-induced anaemia. is possibly the oldest and widely recognised clinical sign of a patent parasitic infection (Soulsby, 1976).


    The derangement in host metabolism is the summation of a multitude of processes which leads to quantitative changes in animal productivity. It consists of the totality of all the modifications that make the difference between health and disease. The effect of a reduction in feed intake in healthy animals is considered first.

    At lower levels of food intake, healthy subjects are able to attain energy balance partly by reducing energy expenditure and by mobilizing fat reserves for energy production indicating the use of non-protein energy sources to meet their energy requirements. As demonstrated (see Chapter 2), this was accomplished by the observed rapid fall in maintenance requirements accompanied by lowered body temperature during starvation or feed restriction. The physiological and/or behavioural strategies employed by energy-restricted subjects for survival are principally based on the reduction in energy expenditure. The findings presented in Chapter 3 indicate a positive correlation between body temperature and digestible organic matter intake (DOMI). This conserving process is a regular adaptive measure in healthy subjects during periods of caloric insufficiency. It concurs with the findings of Shetty (1990); Zwart eta/, (1991) and Ketelaars and Tolkamp (1991). The implication is that feed-restricted animals utilize their nutrient resources more efficiently by reducing body temperature and maintenance requirements to a level proportionate to intake. Several such adaptive physiological responses tend to reduce the metabolic activity of tissues in order to improve the efficient use of resources. The animals are therefore able to maintain nitrogen and energy balance at intake levels reasonably lower than those of ad libitum fed animals (Chapter 2).

    However, these findings are contrary to what has been reported as occuring during infection-induced fever, where metabolic rate is typically not proportionate to intake (Hayashi et al, 1985). Waterlow (1986) showed that the pattern of endogenous fuel substrate utilization differed significantly between healthy feedrestricted subjects and those with a restricted intake caused by an induced infection. Contrary to the depressed values found in Trypanosoma vivax infected goats, no deviation from normal levels was observed in the T3 and T4 concentrations in feedrestricted healthy goats (van Dam, Unpublished). This observation further strengthens the hypothesis that thyroid activity declines following infection with trypanosomiasis, suggesting that other mechanisms might be involved in the regulation of energy metabolism during infection.


    As shown in Chapters 1, 2, 4, and 5 trypanosomiasis studied in different physiological stages of the West African Dwarf (WAD) goats and sheep produces varying responses to feed intake. On average, the infection-mediated anorexia observed in these experiments conforms with earlier findings observed during trypanosomiasis (Ilemobade and Balogun, 1981; Akinbamijo, 1988; Zwart, 1989). The decreased intake is mainly responsible for the negative nitrogen balance and reduced productivity.

    No evidence of a haemorrhagic infection was found during trypanosomiasis in the research reported in this thesis. This observation, confirmed by absence of intestinal and kidney lesions at post-mortem examination, makes nitrogenous losses via intestines or kidneys unlikely (Ingh et al , 1976). In all the studies conducted, the digestive capacity was not affected by trypanosomiasis. The similar faecal nitrogen output obtained in infected and control animals nullifies the possibility of intestinal nitrogenous losses due to infection. The finding that there was no urinary protein agrees completely with post- mortem observations reported in Chapter 2 and no kidney lesions were found.

    In the trypanosomiasis research reported in this thesis, the infection was always accompanied by fever. This is consistent with the fact that protozoal infections are often accompanied by fever which increases the energy expenditure of the infected host. This contention expressed by Baracos et al , (1987) and Cohen and Lambert (1982) was also supported by Verstegen et al , (199 1) who attributed a 25% increase in the maintenance requirement of Trypanosoma vivax infected goats to fever. In the present research, all infected animals became febrile from the onset of infection and maintained the pyrexia throughout the infection. Fever, increased basal metabolic rate (BMR) and heat production have been identified as factors contributing to increased energy demands characteristic of infected subjects (Keusch and Farthing, 1986).

    This thesis indicates that the metabolic costs accompanying the infection (Baracos et W , 1987; Verstegen et al , 1991) and anorexia during trypanosomiasis led to increased lipolysis in the host animal. An increased concentration of serum non- esterified fatty acids (NEFA) was observed in infected subjects, confirming that body fat reserves were being used to bridge the energy gap due to anorexia and increased maintenance requirements (Chapter 1). The observed increase in blood urea concentration indicates that a minimal breakdown of body proteins cannot be excluded. This agrees with the findings of Beisel (1985). No evidence was found of increased ketogenesis or excessive breakdown of body proteins, even when feed intake was as low as 40% of maintenance requirements. However, two cases in which increased concentration of serum ketone bodies following extreme anorexia was observed (Chapter 2) deserve mention. A similar metabolic response was described by Symons (1985) and Beisel (1985) during severe starvation.

    During the post-infection phase, anaemic and anorexic pregnant ewes tended to reduce rate of weight gain and body condition. These derangements during trypanosomiasis have been attributed to a number of factors: a reduction in dry matter intake (Akinbamijo et al , 1990), an increased basal metabolic rate (Zwart et al , 1991; Stephen 1986), an increased catabolism of tissue reserves (Akinbamijo et al , 1992) a reduced nitrogen and energy balance (Zwart et al , 1991; Verstegen et al , 1991) and possibly an uptake of host's nutrient by the parasites (Reynolds, Personal Communications). In the acute phase response and the related wasting physiological events that follow, the increased metabolic rate has severe implications for livestock productivity, such as dam mortality, foetal and neo-natal losses. These three factors attained prominence in earlier reviews on the effect of trypanosomiasis on reproduction (Ogwu and Nuru, 1981; Ogwu et al , 1986; Ikede et al , 1988) and in the findings of Elhassan (1987) and Reynolds and Ekwuruke (1988) in WAD sheep.

    In the present research, infected ewes ending pregnancy with low maternal weights and depressed intake, had lambs with lower birth weights that suffered considerable neonatal mortality. Consequently, 85% of lambs from ewes infected at late pregnancy died within seven days after birth. The relation in non-infected ewes, between lamb birth weight and growth rate and maternal effects of pregnancy nutrition and dam weight at parturition are widely reported (Gibb and Treacher, 1980 & 1982, Pearl 1967, Treacher 1970, Adu and Olaloku, 1979). In the event of a severe nutritional stress, incidences of sporadic abortion have been reported (Osuagwuh and Akpokodje, 1986; Osuagwuh and Aire, 1990). Hence if dam and foetal nutrition is inadequate, it can induce results such as were obtained in infected ewes (Chapter 4). The maternal effects on the low lamb birth weights were reflected in the low weaning weights of the lambs from infected dams.

    In spite of the infection, ewes infected after lambing had sufficient body reserves to meet the daily milk yield observed in all animals during early lactation. Lactation is often associated with an increase in feed intake (Blaxter, 1989), and this may have masked the effect of infection on intake and milk yield during early lactation in the infected dams (Chapter 5). In relation to the live weight pattern, it could be deduced that infected lactating sheep catabolized body reserves to supplement the dietary nutrients required for milk production as established by Gibb and Treacher (1982). Since milk yield did not differ during early lactation, the growth rate did not differ between lamb groups. The difference in milk yield observed during late lactation had no effect on lamb growth rate, as lambs had commenced the weaning process and were supplementing their milk intake with forage.


    As intended, the clinical observations of the low to medium level infection mimic those of the sub-clinical infection usually experienced by grazing stock. No evidence was found of changes in the feed intake and digestive capacity of the hosts post infection. This concurs with the finding of Hawkins and Morris (1978) obtained using graded levels of infection doses, that there is a negative relationship between fluke burden and digestibility coefficients. Considering the infection dose used in this thesis, the infection level was too low to initiate digestive disturbances. The costs of infection (inefficient feed utilization) were evident. This conforms with the reports of Berry and Dargie (1976) and Dargie et al , (1979).

    The sub-clinical fascioliasis had no effect on the voluntary feed intake of open and pregnant Menz ewes. However, this finding conflicts with what occurs during parasitism, where anorexia is reported as one of the earliest symptoms (Berry and Dargie, 1976; Murray and Murray, 1979; Symons, 1985, Keusch and Farthing, 1986; Holmes, 1987; Morris 1988). The explanation of this finding can only be a conjecture: in our experiment, it is probably connected with factors such as breed and age of the host, the viability and number of metacercariae administered and the presence of an undetermined level of pre- infection immunity (Sinclair, 1971; Berry and Dargie, 1976; Leyva et al , 1982).

    The digestive capacity of the ewes was found not to be affected by infection or pregnancy either. This conforms with most findings during parasitism (Dargie et al , 1979; Berry and Dargie, 1976) but contrasts with reports by Holmes (1987) who suggested the possibility of impaired digestive and absorptive processes especially due to loss of intestinal proteins into the gastro-intestinal tract during helminth infections. However, as already noted, in the present study, the similarity of the faecal nitrogen in infected and control animals invalidates the chances of such an occurrence.

    Despite the low to medium level fascioliasis imposed on them, the infected Menz ewes indicated a decline in PCV about eight weeks post-infection. This is similar to the observations of Sinclair (1971) and Dow et al (1968). The decline in PCV post infection substantiated the presence of an infection effect in inoculated ewes.

    At comparable levels of voluntary feed intake, infected ewes retained less nitrogen, gained less weight, and produced lighter lambs and had poorer body condition (Chapter 6). This is probably because of differences in the efficiency of utilization or conversion of feed into desired animal products. The difference in growth rate between infected and healthy goats (Chapter 1) illustrates the nutrient drain that accompanies the infection. Inefficient feed utilization and wasting of this type during parasitic infections is also widely reported in the literature quoted above. The nitrogen retention differed remarkably in the early part of the infection and gradually reverted as the infection progressed. An upturn in PCV observed towards the end of the study may also be related to the acquired resistance phenomenon suggested earlier by Sinclair (1971). The reduced nitrogen retention reported by Dargie et al (1979) at eight weeks post-infection, was principally due to high urinary nitrogen. In our study, the findings with respect to the time schedule, the lower nitrogen retention and high urinary nitrogen observed in the infected ewes, are similar to those reported by Dargie and his co-workers (1979). The observed similarity in feed intake and digestibility in control and infected ewes indicate that other insidious losses must have had a major effect on the overall nitrogen retention and lower rate of weight gain in infected ewes. This is largely borne out by the nitrogen balance and body weight data that put the infected sheep on the lower limit. Although our study provides no clues about the extra nitrogen excreted by infected ewes, its appearance in the urine rather than in faeces confirms the contention that the host's digestive and absorptive capacity was not impaired during the low to medium fascioliasis.

    Live weight gain in the animals was also considerably affected in the infected animals. It has been reported that sheep infected with Fasciola hepatica failed to maintain the rate of body weight gain observed in uninfected counterparts (Reid et al , 1970; Holmes, 1987; Blackburn, 1991). Lamb birth weight was lower in infected ewes than the control ewes. The low nitrogen retention found in infected pregnant ewes strengthens the contention that there was less nitrogen accretion in the foetus. Such deleterious effects of parasitism on the productive potential and the efficient use of resources have been demonstrated earlier (Ogwu et al , 1986;lkede et al , 1988; Reynolds and Ekwuruke, 1988; Akinbamijo et al , 1994).


    In the studies with Trypanosoma and Fasciola spp. reported in this thesis, absence of digestive disturbances was clear but in neither case did infected animals utilize their food as well as non-parasitized controls. The onset of infection coincided with reduced nitrogen retention resulting from a combined effect of reduced voluntary feed intake and/or increased excretion of urinary nitrogen. As productivity is governed not only by the gross intake but also by the efficiency of conversion into desired products, the evidence obtained in this research suggests that the reduced productivity of parasitized animals is the direct result of infection depressing the utilization of feed intake.

    In quantitative terms, less digested nitrogen was retained in the tissues or products of the infected animals. This is typified by the findings reported in the first chapter, where it was shown that trypanosomiasis was responsible for the low growth rate. No carcass analyses were conducted in this research, but other researchers have reported changes in body composition during undernutrition (Wolkers, 1993) and infection (Sykes and Coop, 1976). Both undernutrition and infection were observed in the present research (see Chapters 1 and 2).

    Reproductive wastage generally traceable to infections is considered to be substantial during infection (Osuagwuh and Aire, 1990; Osuagwuh and Akpokoje, 1986). It is usually characterized by embryonic or foetal death, abortion, premature birth, still birth, birth of weak offspring and neonatal deaths (see Chapter 4). It seems rational that if the dam is in good body condition pre-partum, then the offspring will have a good chance of surviving. However, this is often not the case during parasitism. Depending on the severity of infection, if the nutritional stress becomes extreme, most or all of the conditions mentioned above will occur, and reproductive wastage will result. The degree of reproductive wastage is therefore related to the level of dam nutrition and parasite load. Considering the findings of lkede and Losos, (1972) in sheep and Ogwu et al , (1986) in cattle, the possibility of intra-uterine infection cannot be ruled out in this study.

    At sub-clinical levels, infection resulted in an appreciable degree of poor nutrient utilization that may have serious consequences on productivity (Chapters 4 and 6). Infection of pregnant ewes was characterized by low nitrogen retention, poor weight gains, and poor body condition and foetal development culminating in low lamb birth weight. Even when the dam was treated post-partum, the carry-over effects from gestation were reflected in the lamb performance.

    There were no profound effects of infection on lamb growth rates, but infected dams lost more weight at lactation and retained less nitrogen. In the context of livestock health and productivity, parasitism lowers the production potential or offtake of the infected animals. As observed from this thesis, elements of the productivity and reproductive indices mainly growth rate (or weight gain), ewe mortality, abortion ratelfoetal loss, birth weight, weaning weight, neonatal loss, nitrogen retention and body condition, and milk yield were appreciably affected by parasitism. Others which should have been included are weight of offspring weaned per dam, the number of lambs produced and number of lambs born per 100 ewes.

    Concurrent with findings of Ogwu et a] (1986) in cattle, Elhassan, (1987) and Reynolds and Ekwuruke (1988) in sheep, abortion occurred in infected ewes during the third trimester. The effect of chronic clinical or sub-clinical trypanosomiasis on reproduction and fertility such as anoestrus, failure to conceive, poor libido have been reported by the authors cited above. These disorders have a direct bearing on the productivity index (PI) described by Bosman et al (1988) and the reproductive index (RI) described by Burfening et al (1993). According to the indices of productivity described by these workers, the incidence of parasitic diseases in small ruminant husbandry has a multiplier effect on productivity as the two indices (PI and RI) are direct determinants of prolificacy (Gabina, 1988). This implies that the factors affected by parasitism are the determinants of productivity and hence are responsible for the reduction in the expression of the genetic potential and the optimum offtake per livestock unit. As shown by this thesis, the consequences of infection do not stop at morbidity alone but also flow through to incidence of mortality (Anene et al , 1991). In general, the findings in this thesis corroborate the suggestion of Smith et al (1988) that the problem of tropical livestock is clearly not one of inadequate number of livestock units but of low productivity.

    The pathogenesis and clinical observations recorded during this thesis are similar to those frequently seen on the field during natural challenges. The subclinical infection keeps the host in an apparently healthy state but the overall cost of infection on productivity is substantial. A sub-clinical infection is more important to productivity than clinical infection. The latter, when it occurs, is often easily recognized and treated, or death results. In sub-clinical infections, however, such as are present in some breeds with varying degrees of resistance, the effect on the productivity and economics of production can be very grave.

    Based on the findings in this thesis, it can be concluded that feed- restricted healthy animals make physiological adjustments by reducing body temperature and maintenance requirements to compensate for the reduced voluntary feed intake. The body temperature in such subjects is also positively related to the digestible organic matter intake. However, the relationship between DOMI and NRET is not affected by infection or artificial feed restriction.

    The VFI was lower in the acute phase of infection in open, pregnant and dry parasitized animals, leading to reduced NRET and productivity. However, this was not the case during a low to medium fascioliasis in adult ewes: in the latter, the digestive capacity was not affected. However, low NRET and productivity were observed in all cases of infection investigated.
    The infection of pregnant animals resulted in reproductive wastage and low productivity. Milk yield and composition of non-dairy sheep during trypanosomiasis did not after and hence have no effect on the lamb growth rate.


    This research has demonstrated the importance of anorexia and the compensatory role of the accompanying lipolysis in parasitized animals. Nutrient wasting is found to be reinforced by the incidence of fever during trypanosomiasis. A prominent feature in trypanosomiasis, and fascioliasis is the reduced nitrogen retention caused by anorexia and/or increased losses of urinary nitrogen.

    Future work should be directed at unveiling the strategies for feed intake during infection (trypanosomiasis) and the effect of higher levels of infection during fascioliasis. Additional research should be directed towards studies that will identify physiological responses associated with nitrogen metabolism during pathologic conditions.

    A new theory of feed intake regulation in ruminants and its implications for forage quality research.
    Ketelaars, J.J.M.H. ; Tolkamp, B.J. - \ 1994
    In: Proc. 17th Int. Grassland Congr. Palmerston, New Zealand 1993 - p. 702 - 703.
    Maakbaarheid van de Natuur.
    Peeters, E.T.H.M. ; Rooy, P. van; Ketelaars, H. ; Fellinger, M. - \ 1994
    Nieuwsbrief Werkgroep Ecologisch Waterbeheer (1994)20. - 20 p.
    Protein kinase C modulates the motional properties of its lipid cofactor DPH-diacylglycerol.
    Pap, E.H.W. ; Borst, J.W. ; Ketelaars, M. ; Hoek, A. van; Visser, A.J.W.G. - \ 1994
    Proceedings of spie 2137 (1994). - ISSN 1996-756X - p. 736 - 740.
    Protein kinase C modulates motional properties of its lipid cofactor DPH-diacylglycerol.
    Pap, E.H.W. ; Borst, J.W. ; Ketelaars, M. ; Hoek, A. van; Visser, A.J.W.G. - \ 1994
    In: Time-resolved laser spectroscopy in biochemistry IV, J.R. Lakowicz (ed.). Proc. Int. Soc. Optical Engineering SPIE. Los Angeles, USA (1994) Vol.2137 - p. 736 - 740.
    Voluntary intake of digestible organic matter and fasting heat production of West African Dwarf goats and Swifter sheep.
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. ; Hofs, P. - \ 1994
    Small Ruminant Research 15 (1994). - ISSN 0921-4488 - p. 45 - 54.
    Short term feed intake as part of a long term feeding strategy.
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. - \ 1994
    In: Proc. 45th Annual Meeting EAAP, Session 2: Animal strategies for optimizing their nutrition, Edinburgh (1994) N2.3, 7 pp
    Foraging behaviour programs in ruminants.
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. - \ 1994
    In: CSAS annual meeting Livestock production in the 21st century: priorities and research needs. P.A. Thacker (ed.). Univ. Saskatchewan, Saskantoor, Canada - p. 11 - 23.
    Efficiency of energy utilization in cattle given food ad libitum: predictions according to the ARC system and practical consequences.
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. - \ 1994
    Animal Production 59 (1994). - ISSN 0003-3561 - p. 43 - 47.
    Why ruminants regulate their feed intake? And how?
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. - \ 1993
    In: Paper Int. Foraging Behaviour Workshop, Aberdeen, UK (1993) 13 pp
    Theories of feed intake regulation in ruminants (Theorien zur Regulation der Futteraufnahme bei Wiederkauern).
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. - \ 1993
    In: Proc. Soc. Nutrition Physiology, Giesecke, Deutschland, Band 1. Göttingen - p. 42 - 48.
    The effect of ad libitum feeding on the efficiency of energy utilization in growing and lactating cattle.
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. - \ 1993
    Animal Production 56 (1993). - ISSN 0003-3561 - p. 431 - 432.
    The effect of ad lib feeding on the efficiency of energy utilization in growing and lactating cattle.
    Tolkamp, B.J. ; Ketelaars, J.J.M.H. - \ 1993
    In: Proc. Winter meeting Brit. Soc. Animal production, Scarborough (1993) 55a-55b
    Produktie en herbenutting van endogeen eiwit in de dunne darm van het schaap. Effect van rantsoeneiwit en celwandgehalte.
    Vliet, H.C.M. van; Doorn, C.E.A. van; Brakel, C.E.P. van; Voigt, J. ; Bruchem, J. van; Ketelaars, J.J.M.H. ; Tamminga, S. - \ 1993
    In: Verslag 18e studiedag Nederlandstalige Voedingsonderzoekers Gent (1993)
    Produktie en herbenutting van endogeen eiwit in de dunne darm van het schaap: effect van het rantsoeneiwit en het celwandgehalte.
    Vliet, H.C.M. van der; Doorn, C.E.A. van; Brakel, C.E.P. van; Voigt, J. ; Bruchem, J. van; Ketelaars, J.J.M.H. ; Tamminga, S. - \ 1993
    In: Verslag 18e Studiedag Nederlandstalige Voedingsonderzoekers, Gent (1993)
    Flow of endogenous protein along the gastro-intestinal tract of sheep fed on whole grass hay and hay-concentrate diets.
    Voigt, J. ; Bruchem, J. van; Lammers-Wienhoven, S.C.W. ; Bongers, L.J.G.M. ; Schönhusen, U. ; Valkenburg, G.W. ; Ketelaars, J.J.M.H. ; Tamminga, S. - \ 1993
    Proceedings of the society of nutritional physiology (1993). - p. 63 - 63.
    Flow of endogenous protein along the gastrointestinal tract of sheep fed on whole grass hay and hay-concentrate diets.
    Voigt, J. ; Bruchem, J. van; Lammers-Wienhoven, S.C.W. ; Bongers, L.J.G.M. ; Schönhusen, U. ; Valkenburg, G.W. ; Ketelaars, J.J.M.H. ; Tamminga, S. - \ 1993
    In: Abstract Soc. Nutrition Physiology 1 - p. 63 - 63.
    Produktie en herbenutting van endogeen eiwit in de dunne darm van het schaap - Effect van het rantsoeneiwit en het celwandgehalte.
    Brakel, C.E.P. van; Voigt, J. ; Bruchem, J. van; Ketelaars, J.J.M.H. ; Tamminga, S. - \ 1992
    In: Verslag 17e Studiedag Nederlandstalige Voedingsonderzoekers, Zeewolde. IVVO-DLO rapport 239 - p. 11 - 12.
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