Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

Current refinement(s):

Records 1 - 20 / 48

  • help
  • print

    Print search results

  • export

    Export search results

  • alert
    We will mail you new results for this query: keywords==urea
Check title to add to marked list
Effect of Microbial Interaction on Urea Metabolism in Chinese Liquor Fermentation
Wu, Qun ; Lin, Jianchun ; Cui, Kaixiang ; Du, Rubin ; Zhu, Yang ; Xu, Yan - \ 2017
Journal of Agricultural and Food Chemistry 65 (2017)50. - ISSN 0021-8561 - p. 11133 - 11139.
ethanol fermentation - ethyl carbamate - Lysinibacillus sphaericus - Saccharomyces cerevisiae - spontaneous food fermentation - urea

Urea is the primary precursor of the carcinogen ethyl carbamate in fermented foods. Understanding urea metabolism is important for controlling ethyl carbamate production. Using Chinese liquor as a model system, we used metatranscriptome analysis to investigate urea metabolism in spontaneous food fermentation processes. Saccharomyces cerevisiae was dominant in gene transcription for urea biosynthesis and degradation. Lysinibacillus sphaericus was dominant for urea degradation. S. cerevisiae degraded 18% and L. sphaericus degraded 13% of urea in their corresponding single cultures, whereas they degraded 56% of urea in coculture after 12 h. Compared to single cultures, transcription of CAR1, DAL2, and argA, which are related to urea biosynthesis, decreased by 51, 36, and 69% in coculture, respectively. Transcription of DUR1 and ureA, which are related to urea degradation, increased by 227 and 70%, respectively. Thus, coexistence of the two strains promoted degradation of urea via transcriptional regulation of genes related to urea metabolism.

Refining a model-based assessment strategy to estimate the ammonia emission from floors in dairy cow houses
Snoek, Dennis J.W. - \ 2016
Wageningen University. Promotor(en): Peter Groot Koerkamp, co-promotor(en): Nico Ogink; Hans Stigter. - Wageningen : Wageningen University - ISBN 9789462578852 - 182
dairy cows - stalls - ammonia emission - floors - modeling - mitigation - sensors - ph - temperature - urea - melkkoeien - stallen - ammoniakemissie - vloeren - modelleren - mitigatie - temperatuur - ureum

Ammonia (NH3) emission is still high, and agriculture is still the dominant contributor. In The Netherlands, the NH3 emission from dairy cow houses is one of the most important sources. A lot of research has been conducted to understand and model NH3 emission, to measure it, and to reduce it using identified and developed reduction measures. However, our understanding of how to measure and how to reduce the NH3 emission is still limited. In addition, the set emission ceilings were lowered for 2020.

The objective of this thesis was to refine a model-based assessment strategy to estimate the ammonia emission from floors in dairy cow houses. First the most important input variables and process parameters were identified with a sensitivity analysis in currently available mechanistic NH3 emission models and theory. It was concluded that five puddle related input variables caused the largest variation in NH3 emission estimation, being the puddle pH, depth (Dp), urinary urea nitrogen concentration (UUN), surface area (Ap), and temperature (Tliq). For each input variable the available data was scarce, and it was therefore recommended to measure these five most important variables in practice. However, measurement methods were hardly available. Therefore, sensors were chosen, new measurement methods were developed, and these were combined in a protocol to measure the pH, Dp, UUN, Ap and Tliq of fresh, random and manually created urine puddles in commercial dairy cow houses.

In total 16 commercial dairy cow houses were assessed in a factorial experimental setup based on four floor-management types in two Seasons, with PREclean treatment. PREclean represented intense-floor-cleaning that was compared to on-farm manure scraping. A V-shaped asphalt floor had significantly larger values for both Ap (1.04 m2) and Dp (1.5 mm) than did the slatted and grooved floors (0.76 m2, 0.93 mm). For both Ap and Dp the variation within a farm was large, but was negligible between farms. The Dp values and variation were 3 to 6 times larger than currently assumed. With PREclean treatment the Dp resulted in about 3 times lower values compared to the on-farm scraping. In short, the potential NH3 emission reduction of good floor cleaning is large. Overall mean values were 4.27 kg m-3 for UUN, an initial pH(t=0) of 8.3, both in fresh puddles, and a pH(t=ξ) of 9.0 for random puddles at a random time. For UUN both the variation within and between farms was large, whereas the variation for pH was small. Both the mean UUN and pH showed lower values than currently assumed. In a separate 4 h time series experiment at 3 commercial farms was shown that the pH, on average, quickly increased initially, declined after 1 h and then became stable. The calculated NH3 in kg puddle-1 showed a huge range and was considerably larger than currently assumed for the reference situation.

Compared to the aforementioned sensitivity analysis outcome, the UUN range at farm level is both slightly smaller and shifts to slightly lower values, while for Dp the range and values are both larger. These two variables caused the largest variation in the estimated NH3 emissions, and not the pH. In conclusion, these two variables certainly need to be measured in individual commercial dairy cow houses to estimate the NH3 emission. For Ap, pH and Tair the measured ranges at farm level were less large. The pH turns out to be fairly stable in commercial cow houses and, related to that, it causes less variation in the estimated NH3 emission. Nevertheless, the pH still ranks as the third most important variable, and therefore needs to be measured in individual cow houses. The Ap is fairly stable between farms, but varies within farms and it still has a significant effect on the NH3 emission. The floor design clearly affects the puddle area Ap. Therefore, it is not necessary to measure Ap at each individual farm, but it is sufficient to measure the Ap in only one commercial cow house per floor design. The Tair variable is of limited importance compared to the aforementioned four variables, but it is still significant.

Nieuwe voedingsschema’s phalaenopsis voor veranderde teeltwijze : recirculatie, productieverhoging, teeltverkorting
Kromwijk, Arca ; Blok, Chris - \ 2016
horticulture - greenhouse horticulture - pot plants - phalaenopsis - recirculating systems - cropping systems - nutrients - crop production - urea - sodium - zinc - crop growth stage - agricultural research

De teelt van phalaenopsis is in de afgelopen vijftien jaar zo sterk veranderd, dat de praktijk niet goed meer uit de voeten kon met de voedingsschema’s uit de jaren negentig. Onderzoekers van Wageningen UR Glastuinbouw hebben daarom nieuwe schema’s ontwikkeld, die inmiddels op grote schaal toepassing vinden. Het gaat om schema’s voor opkweek (vegetatief) en afkweek (generatief) in bedrijfssituaties met en zonder recirculatie.

Dietary protein, blood pressure and mortality : the value of repeated measurements
Tielemans, S.M.A.J. - \ 2016
Wageningen University. Promotor(en): Marianne Geleijnse; Daan Kromhout, co-promotor(en): Hendriek Boshuizen. - Wageningen : Wageningen University - ISBN 9789462577916 - 169 p.
cardiovascular diseases - blood pressure - dietary protein - mortality - cardiovascular disorders - hypertension - urea - meta-analysis - antihypertensive agents - plant protein - animal protein - hart- en vaatziekten - bloeddruk - voedingseiwit - mortaliteit - hart- en vaatstoornissen - hypertensie - ureum - meta-analyse - antihypertensiva - plantaardig eiwit - dierlijk eiwit

Cardiovascular diseases (CVD) are the main cause of death worldwide. In 2012, about 17.5 million people died from CVD, accounting for 30% of all deaths. High blood pressure (BP) is a major cardiovascular risk factor, which was responsible for 10.4 million deaths in 2013. Diet and lifestyle play an important role in the etiology of hypertension. Maintenance of a desirable body weight, physical activity, and low intake of alcohol and salt are well-known measures to avoid high BP. Whether dietary protein, or more specifically plant and animal protein, could contribute to maintaining a healthy BP is less clear. The association between BP and CVD mortality has been extensively investigated. BP in prospective studies can be analyzed using different approaches, such as single BP (measured at one moment in time), single BP adjusted for regression dilution, average BP, and trajectories of BP. It is not yet clear which of these approaches is to be preferred for CVD risk prediction.

This thesis is centered on BP as a major cardiovascular risk factor. In the first part (Chapter 2, 3 and 4), the relation of dietary protein intake with BP level and change was examined. In the second part (Chapter 5 and 6), various approaches for analyzing repeated BP measurements were compared in relation to CVD and all‑cause mortality risk. The final chapter discusses the main findings and their implications.

Chapter 2 describes the association of 24-h urinary urea excretion, as a biomarker of total protein intake, with 9-year incidence of hypertension. We analyzed data of ~4000 men and women aged 28–75 years, who participated in the Prevention of Renal and Vascular Endstage Disease (PREVEND) study, a prospective cohort study. BP was measured four times during 1997–2009 and participants were followed for hypertension incidence, defined as BP ≥140/90mmHg or use of antihypertensive medication. Urea excretion was assessed in two consecutive 24-h urine collections at baseline and approximately 4 years later, from which total protein intake was estimated. Protein intake based on 24-h urinary urea excretion was not associated with incident hypertension.

Chapter 3 presents findings for long-term total, animal and plant protein intake in relation to 5‑year BP change. Analyses were based on 702 observations of 272 men who participated in the Zutphen Elderly Study. Participants did not use antihypertensive medication and were initially free of CVD. Physical and dietary examinations were performed in 1985, 1990, 1995, and 2000. BP was measured twice at each examination and protein intake was assessed using the cross-check dietary history method. The upper tertiles of plant protein intake were associated with a mean 5‑year change in systolic BP of ‑2.9 mmHg (95% CI: ‑5.6, ‑0.2), compared with the bottom tertile. Total and animal protein intake was not associated with BP.

Chapter 4 describes a meta‑analysis of 12 observational studies and 17 randomized controlled trials (RCTs) of dietary protein, including animal and plant protein, in relation to BP. Protein intake in prospective cohort studies was not associated with incident hypertension. For RCTs that used carbohydrate as a control treatment, the pooled BP effect was ‑2.1 mmHg systolic (95% CI: ‑2.9, ‑1.4) for a weighted mean contrast in protein intake of 41 grams per day. There was no differential effect of animal and plant protein on BP.

Chapter 5 describes repeated BP measures and their association with CVD and all‑cause mortality and life years lost in two prospective and nearly extinct cohorts of middle-aged men, the Minnesota Business and Professional Men Study (n=261) and the Zutphen Study (n=632). BP was measured annually during 1947–1957 in Minnesota and 1960–1970 in Zutphen. After 10 years of BP measurements, men were followed until death on average 20 years later. Each 25-mmHg increase in average SBP was associated with a 49% to 72% greater CVD mortality risk, 34% to 46% greater all-cause mortality risk and 3 to 4 life years lost. Four systolic BP trajectories were identified, in which mean systolic BP increased by 5 to 49 mmHg in Minnesota and 5 to 20 mmHg in Zutphen between age 50 and 60. In Zutphen, a 2-times greater CVD and all-cause mortality risk and 4 life years lost were observed when comparing trajectories. In Minnesota, associations were twice as strong. BP trajectories were the strongest predictors of CVD mortality and life years lost in Minnesota men, whereas in Zutphen men, the average BP was superior to other measures.

Chapter 6 presents findings for average BP and BP trajectories in relation to CVD and all-cause mortality, taking into account antihypertensive medication. A total of 762 participants aged ≥50 years of the Rancho Bernardo Study were examined five times from 1984 to 2002 and monitored for cause‑specific mortality from 2002 to 2013. Each 20‑mmHg increment in average systolic BP was associated with 35% greater CVD mortality and 25% greater all-cause mortality risk. We identified four trajectories for systolic BP for which BP increases ranged from 5 to 12 mmHg between age 60 and 70. In individuals who belonged to the higher trajectories, 2‑3 times greater CVD mortality and 1.5-times greater all-cause mortality risks were observed, compared to those who belonged to the lowest trajectory. Long-term systolic BP trajectories and average systolic BP were both significant predictors of CVD and all-cause mortality. The associations were not modified by antihypertensive medication.

As described in Chapter 7, various approaches were used to study the relation between protein intake and BP. Findings from individual studies and a meta-analysis suggest that dietary protein per se does not affect BP within the range of intake generally consumed in the Netherlands. Replacing carbohydrates by protein, however, has a beneficial effect on BP.

Moreover, this thesis showed that BP trajectories are not superior to average BP in predicting CVD and all-cause mortality. A few repeated BP measurements, e.g. three or four, are likely to be sufficient for obtaining a reliable average BP and had a similar predictive value for mortality compared to BP trajectories. Therefore, average BP can be considered the most practical tool for estimating mortality risk.

Effect of protein provision via milk replacer or solid feed on protein metabolism in veal calves
Berends, H. ; Borne, J.J.G.C. van den; Røjen, B.A. ; Hendriks, W.H. ; Gerrits, W.J.J. - \ 2015
Journal of Dairy Science 98 (2015)2. - ISSN 0022-0302 - p. 1119 - 1126.
heavy preruminant calves - amino-acids - energy-metabolism - rumen development - dairy-cattle - nitrogen - urea - growth - performance - deposition
The current study evaluated the effects of protein provision to calves fed a combination of solid feed (SF) and milk replacer (MR) at equal total N intake on urea recycling and N retention. Nitrogen balance traits and [15N2]urea kinetics were measured in 30 calves (23 wk of age, 180 ± 3.7 kg of body weight), after being exposed to the following experimental treatments for 11 wk: a low level of SF with a low N content (SF providing 12% of total N intake), a high level of SF with a low N content (SF providing 22% of total N intake), or a high level of SF with a high N content (SF providing 36% of total N intake). The SF mixture consisted of 50% concentrates, 25% corn silage, and 25% straw on a dry matter basis. Total N intake was equalized to 1.8 g of N·kg of BW-0.75·d-1 by adjusting N intake via MR. All calves were housed individually on metabolic cages to allow for quantification of a N balance of calves for 5 d, and for the assessment of urea recycling from [15N2]urea kinetics. Increasing low-N SF intake at equal total N intake resulted in a shift from urinary to fecal N excretion but did not affect protein retention (0.71 g of N·kg of BW-0.75·d-1). Increasing low-N SF intake increased urea recycling but urea reused for anabolism remained unaffected. Total-tract neutral detergent fiber digestibility decreased (-9%) with increasing low-N SF intake, indicating reduced rumen fermentation. Increasing the N content of SF at equal total N intake resulted in decreased urea production, excretion, and return to ornithine cycle, and increased protein retention by 17%. This increase was likely related to an effect of energy availability on protein retention due to an increase in total-tract neutral detergent fiber digestion (>10%) and due to an increased energy supply via the MR. In conclusion, increasing low-N SF intake at the expense of N intake from MR, did not affect protein retention efficiency in calves. Increasing the N content of SF at equal total N intake decreased urea production, increased protein retention, and coincided with improved fiber degradation. Therefore, results suggest that low N availability in the rumen limits microbial growth and rumen fermentation in calves fed low-N SF (93 g of CP/kg of DM), and this effect cannot be compensated for by recycling of urea originating from MR.
Stikstofverliezen beter inschatten
Spek, J.W. ; Bannink, A. ; Dijkstra, J. - \ 2013
Veeteelt 30 (2013)17. - ISSN 0168-7565 - p. 20 - 22.
melkveehouderij - stikstofverliezen - excretie - melksamenstelling - ureum - melkveevoeding - voersamenstelling - eiwitgehalte - dairy farming - nitrogen losses - excretion - milk composition - urea - dairy cattle nutrition - feed formulation - protein content
Hoe kan het melkureumgehalte beter worden benut als maat voor stikstofverliezen in de urine? Onderzoekers van WUR concluderen dat stikstofverliezen in de urine beter zijn in te schatten met een combinatie van factoren, zoals het melkureumgehalte en het zout- en eiwitgehalte in het rantsoen.
Variation of milk urea in dairy cattle : a study on factors that affect the relationship between urea concentration in milk and urea excretion in urine
Spek, J.W. - \ 2013
Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): Jan Dijkstra; Andre Bannink. - S.l. : s.n. - ISBN 9789461736642 - 156
melkkoeien - melkvee - ureum - melk - concentratie - urinering - excretie - stikstof - meta-analyse - natriumchloride - opname (intake) - diervoeding - rundveevoeding - voedingsfysiologie - dairy cows - dairy cattle - urea - milk - concentration - urination - excretion - nitrogen - meta-analysis - sodium chloride - intake - animal nutrition - cattle feeding - nutrition physiology

The aim of this thesis was to increase the applicability of milk urea nitrogen concentration (MUN) as a predictor of urinary urea nitrogen excretion (UUN) by identifying and quantifying factors that can explain variation in MUN that is not related to UUN. A literature study was conducted in order to identify these factors that affect the relationship between MUN and UUN. In this literature review a number of factors were established that affect the relationship between MUN and urinary N-excretion (UN) or UUN, such as dietary crude protein content (CP), intake of dietary salt and water, body weight, diurnal variation in plasma urea nitrogen concentration (PUN), exchange of urea between blood and milk, and heritability of MUN. Results of a quantitative meta-analysis where the effect of various physiological and dietary factors on the relationship between MUN and UN or UUN were studied confirmed the fact that CP affects the relationship between MUN and UUN and showed that by using information on MUN and CP more variation in UUN could be explained compared to using information on either MUN or CP alone. One of the factors established in the literature review that can affect the relationship between MUN and UUN is dietary salt content or drink water intake. In order to quantify the effect of dietary salt on MUN and UUN an experiment was carried out that investigated the effect of four dietary levels of sodium chloride (NaCl) on urea levels in blood plasma and milk and on UN and UUN. The results from this trial clearly showed a negative relationship between dietary NaCl content and MUN whereas UUN was not affected by NaCl intake and UN was slightly increased by increasing NaCl intake levels. The question arose whether the effect of dietary salt on MUN would be similar at high and low dietary protein levels as the renal mechanism of excretion and reabsorption of urea is affected by both dietary protein and salt intake. Therefore, the interaction between dietary salt and protein on UUN was tested in an experiment with two CP levels and two dietary NaCl levels. No interaction between dietary NaCl and CP on MUN was observed. However, the relationship between MUN and UUN was altered by the effect of salt intake. The literature review showed that diurnal variation in PUN and MUN can be substantial, and that this variation depends on factors such as time and frequency of feeding and milking. Insight in the dynamics of urea transport between blood of milk is important in order to model and predict variation in MUN over time under various feeding and milking regimes. To obtain quantitative insight in urea fluxes between blood and milk two experiments were conducted in which urea transport from blood to milk and vice versa was investigated by means of pulse dose injections of labeled [15N15N]urea in milk cisterns at various time intervals before milking. The results showed a rapid distribution of injected labeled urea throughout the milk in the mammary gland and substantial urea transport from milk to blood.

It is concluded that various factors that are discussed in this thesis contribute to variation in MUN that is not related to UUN. Taking these factors into account increases the applicability of MUN as a predictor of UUN.

Dietary nitrate supplementation reduces methane emission in beef cattle fed sugarcane-based diets
Hulshof, R.B.A. ; Berndt, A. ; Gerrits, W.J.J. ; Dijkstra, J. ; Zijderveld, S.M. van; Newbold, J.R. ; Perdok, H.B. - \ 2012
Journal of Animal Science 90 (2012)7. - ISSN 0021-8812 - p. 2317 - 2323.
rumen fermentation - sheep - methanogenesis - manipulation - mitigation - livestock - nitrite - dairy - urea - wall
The objective of this study was to determine the effect of dietary nitrate on methane emission and rumen fermentation parameters in Nellore × Guzera (Bos indicus) beef cattle fed a sugarcane based diet. The experiment was conducted with 16 steers weighing 283 ± 49 kg (mean ± SD), 6 rumen cannulated and 10 intact steers, in a cross-over design. The animals were blocked according to BW and presence or absence of rumen cannula and randomly allocated to either the nitrate diet (22 g nitrate/kg DM) or the control diet made isonitrogenous by the addition of urea. The diets consisted of freshly chopped sugarcane and concentrate (60:40 on DM basis), fed as a mixed ration. A 16-d adaptation period was used to allow the rumen microbes to adapt to dietary nitrate. Methane emission was measured using the sulfur hexafluoride tracer technique. Dry matter intake (P = 0.09) tended to be less when nitrate was present in the diet compared with the control, 6.60 and 7.05 kg/d DMI, respectively. The daily methane production was reduced (P <0.01) by 32% when steers were fed the nitrate diet (85 g/d) compared with the urea diet (125 g/d). Methane emission per kilogram DMI was 27% less (P <0.01) on the nitrate diet (13.3 g methane/kg DMI) than on the control diet (18.2 g methane/kg DMI). Methane losses as a fraction of gross energy intake (GEI) were less (P <0.01) on the nitrate diet (4.2% of GEI) than on the control diet (5.9% of GEI). Nitrate mitigated enteric methane production by 87% of the theoretical potential. The rumen fluid ammonia-nitrogen (NH3-N) concentration was significantly greater (P <0.05) for the nitrate diet. The total concentration of VFA was not affected (P = 0.61) by nitrate in the diet, while the proportion of acetic acid tended to be greater (P = 0.09), propionic acid less (P = 0.06) and acetate/propionate ratio tended to be greater (P = 0.06) for the nitrate diet. Dietary nitrate reduced enteric methane emission in beef cattle fed sugarcane based diet.
Sulphur levels in saliva as an estimation of sulphur status in cattle: a validation study
Dermauw, V. ; Froidmont, E. ; Dijkstra, J. ; Boever, J.L. de; Vyverman, W. ; Debeer, A.E. ; Janssens, G.P.J. - \ 2012
Archives of Animal Nutrition 66 (2012)6. - ISSN 1745-039X - p. 507 - 513.
rumen fluid - sheep - metabolism - sulfate - plasma - roughage - blood - feed - urea - cows
Effective assessment of sulphur (S) status in cattle is important for optimal health, yet remains difficult. Rumen fluid S concentrations are preferred, but difficult to sample under practical conditions. This study aimed to evaluate salivary S concentration as estimator of S status in cattle. Saliva and rumen fluid samples were collected from dairy cows (n = 16) as well as samples of different feedstuffs offered to the animals. The N and S concentrations were determined using the Dumas technique. The average dietary N and S content were calculated as well as N:S ratio of saliva, rumen fluid and diet. Salivary S concentrations could not predict rumen fluid or dietary S concentrations (p > 0.05). The log transformed salivary N:S ratio (x) could predict the rumen fluid N:S ratio (y) with a linear equation of y = 9.83 (±4.59) x + 0.39 (±4.56) (r = 0.497, p = 0.05), but left too much residual variation to serve as reliable predictor. Further research should investigate this relationship in the search for an S status estimator.
Lignin based controlled release coatings
Mulder, W.J. ; Gosselink, R.J.A. ; Vingerhoeds, M.H. ; Harmsen, P.F.H. ; Eastham, D. - \ 2011
Industrial Crops and Products 34 (2011)1. - ISSN 0926-6690 - p. 915 - 920.
slow-release - kraft lignin - fertilizer - formulations - urea - polymers - sorghum
Urea is a commonly used fertilizer. Due to its high water-solubility, misuse easily leads to excess nitrogen levels in the soil. The aim of this research was to develop an economically feasible and biodegradable slow-release coating for urea. For this purpose, lignin was selected as coating material. From four commercially available lignins, two lignosulfonates (Wafex P and Borresperce), a softwood kraft (Indulin AT) and soda flax lignin (Bioplast), the latter showed the best potential with respect to film forming properties. Bioplast dispersions up to a dry matter content of 50% are processable. However, high losses during processing resulted in thin coating layers on the urea granules. To reduce urea release, hydrophobic compounds and crosslinkers were added to the Bioplast dispersions. Addition of alkenyl succinic anhydride (ASA) significantly decreased the release of urea in water. However, complete release of urea still occurred within one hour, which can be explained by a low reactivity of the selected compounds towards lignin, too low percentages of applied coating or negative effects of the selected compounds on the film forming process. In addition, urea partly dissolves in the aqueous lignin dispersions due to its high water-solubility. This causes incorporation of urea in the lignin layer, which results in coatings with a low water resistance. This was improved by application of an inner coating layer with high dry matter content. In conclusion, lignin shows high potential as coating material. For industrial application, more insight in the film forming properties is desired.
Waarde van melkureum als schatter stikstofexcretie : talrijke factoren beïnvloeden relatie tussen melkureum en stikstof
Spek, J.W. ; Bannink, A. ; Dijkstra, J. - \ 2011
Veeteelt 28 (2011)10. - ISSN 0168-7565 - p. 40 - 41.
melkveehouderij - melksamenstelling - ureum - stikstof - excretie - urine - ammoniak - dairy farming - milk composition - urea - nitrogen - excretion - ammonia
Het melkureum gehalte geldt in Nederland als instrument voor het schatten van de stikstofexcretie van melkvee. Wageningse onderzoekers gingen na hoe het melkureumgehalte beter gebruikt kan worden als indicator en hoe een aantal factoren verschillen in melkureumgehalte.
Lammerensterfte, leverbot en ureum bij melkschapen
Verkaik, J.C. ; Smolders, G. - \ 2010
Lelystad : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 417) - 27
biologische landbouw - schapenhouderij - mortaliteit - lammeren - schapen - leverbot - ureum - geboorte - agrarische bedrijfsvoering - quarantaine - eiwitopname - zware metalen - organic farming - sheep farming - mortality - lambs - sheep - liver flukes - urea - birth - farm management - quarantine - protein uptake - heavy metals
The monitored lamb mortality at organic dairy sheep farms is relativly high with big differences. Mortality over 10% is caused by poor management and infectious abortions. Short term improvements needs a structured approach. Treatment of the dairy sheep is limited to the dry period. Avoiding infection by housing ewes in early lactation appears effective. Liver fluke is well predictable on the prognosis and the fluke and grazing history. The time between infection intake and appearance in blood or dung makes these researches risky. Urea appears dependable upon the amount of protein fed. Protein wastage reduces when more energy is fed.
The impact of elevated water ammonia concentration on physiology, growth and feed intake of African catfish (Clarius gariepinus)
Schram, E. ; Roques, J.A.C. ; Abbink, W. ; Spanings, T. ; Vries, P. de; Bierman, S.M. ; Vis, J.W. van de - \ 2010
Aquaculture 306 (2010)1-4. - ISSN 0044-8486 - p. 108 - 115.
acid-base regulation - stress-response - environmental ammonia - na+/k+-atpase - fish gill - excretion - urea - toxicity - osmoregulation - paradigm
The threshold concentration for NH3 in rearing water of African catfish (Clarias gariepinus) was assessed. African catfish with an initial mean (SD) weight of 141.0 (24) g were exposed to five different Tamm [sum of NH3 and NH4+] concentrations: 0.37 (Control), 1.06, 2.12, 5.16 and 19.7 mM, which concurs with NH3 concentrations of 4 (Control), 14, 38, 176 and 1084 µM. Plasma concentrations of NH4+, cortisol, glucose and lactate, plasma osmolality, gill morphology, branchial Na+/K+-ATPase activity, feed intake and specific growth rate were monitored. No effect of water NH3 on plasma NH4+ concentrations was detected. Feed intake and specific growth rate were severely affected at exposure to water NH3 concentrations above 90 µM (calculated EC10 values: 89 and 122 µM). No major disturbances in physiological blood parameters were observed at these NH3 concentrations, but gill morphology (a remarkably sensitive stress indicator) deteriorated significantly. Based on the lower limit of the 95% confidence interval for EC10, we advise for African catfish not to exceed a water NH3 concentration of 24 µM (0.34 mg NH3-N/L). This finding is relevant for design and management of African catfish production systems.
Individueel en gericht stimuleren zorgt voor lager melkureumgehalte
Ham, A. van den - \ 2010
Agri-monitor 2010 (2010)01-04-2010. - ISSN 1383-6455
melkveehouderij - ureum - melkproductie - agrarische bedrijfsvoering - dairy farming - urea - milk production - farm management
Als agrarische ondernemers individueel gestimuleerd worden om bedrijf en milieu te combineren levert dat goede resultaten op voor beide doeleinden. Een voorbeeld is het melkureumgehalte. Het kan vaak en gemakkelijk worden gemeten en kan dienen als snelle signalering, waardoor de melkveehouder beter bij kan sturen.
Ureum als instrument om eiwitvoeding te sturen nog niet betrouwbaar: Kengetal ureumgehalte beter benutten
Spek, J.W. ; Bannink, A. ; Dijkstra, J. - \ 2009
Veeteelt 26 (2009)6. - ISSN 0168-7565 - p. 28 - 29.
melkveehouderij - melksamenstelling - ureum - rundveevoeding - dairy farming - milk composition - urea - cattle feeding
Wat kunnen melkveehouders met het ureumgehalte in melk? Het kengetal zegt iets over de stikstofbenutting, maar is als instrument om de eiwitvoeding van melkkoeien te sturen nu nog onvoldoende betrouwbaar. Wageningse onderzoekers pogen daar verbetering in te brengen
Bladvertering stimuleren is moeilijk, maar helpt
Heijne, B. ; Jong, P.F. de; Kohl, J. - \ 2007
De Fruitteelt 97 (2007)2. - ISSN 0016-2302 - p. 10 - 11.
fruitteelt - boomgaarden - ascosporen - bladschimmels - compostering - stemphylium - ureum - vinasse - plantenziekten - gewasbescherming - toegepast onderzoek - fruit growing - orchards - ascospores - phylloplane fungi - composting - urea - plant diseases - plant protection - applied research
De bestrijding van schimmels met fungiciden in boomgaarden in de herfst is gevaarlijk vanwege resistentieontwikkeling. Vinasse en ureum stimuleren de bladvertering enorm. Bovendien remmen ze de productie van ascosporen. Zo ontstaan er minder schurftschimmel en zwartvruchtrotschimmel. Ook sanitaire maatregelen zoals bladversnippering en poetsen blijken effectief te werken. De praktijktoepassing van sanitaire maatregelen kent nog veel beperkingen en hangt voornamelijk af van een droog moment na de bladvalperiode
De fokwaarde voor melkureum als maat voor de efficiëntie van de eiwitbenutting door melkkoeien = The breeding value for milkurea as predictor for the efficiëncy of protein utilization in dairy cows
Sebek, L.B.J. ; Riel, J.W. van - \ 2007
Lelystad : Animal Sciences Group (Rapport / Animal Sciences Group 81) - 16
melkkoeien - melkveehouderij - fokwaarde - ureum - eiwit - stikstof - excretie - dairy cows - dairy farming - breeding value - urea - protein - nitrogen - excretion
De fokwaarde voor melkureum kent geen verband met de efficiëntie van de eiwitbenutting. Daardoor is het niet mogelijk om de N excretie van melkkoeien te verminderen via het fokken op melkkoeien met een erfelijk bepaald laag melkureumgehalte
Felinine stability in the presence of selected urine compounds
Rutherfurd, S.M. ; Kitson, T.M. ; Woolhouse, A.D. ; McGrath, M.C. ; Hendriks, W.H. - \ 2007
Amino Acids 32 (2007)2. - ISSN 0939-4451 - p. 235 - 242.
carbamylation - identification - cheese - flavor - serum - acid - urea
The stability of felinine, an amino acid present in feline urine, was investigated. Synthetic felinine was unstable in the urine of a selection of mammals. Felinine was found to stable in feline urine in which urea had been degraded. Synthetic felinine was found to react specifically with urea and did not react with urea analogues such as biuret or thiourea or other nucleophilic compounds such as ammonia which is more nucleophilic or acetamide and water which are less nucleophilic than urea. The reaction of urea and felinine was independent of pH over the range of 3¿10. Urea did not react with N-acetyl-felinine suggesting a felinine N-terminal interaction with urea. Mass spectral analysis of the reaction products showed the presence of carbamylated felinine and fragmentation ions derived from carbamyl-felinine. The physiological relevance of felinine carbamylation is yet to be determined.
Exploring options to combine high yields with high nitrogen use efficiencies in irrigated rice in China
Jing, Q. ; Bouman, B.A.M. ; Hengsdijk, H. ; Keulen, H. van; Cao, W. - \ 2007
European Journal of Agronomy 26 (2007)2. - ISSN 1161-0301 - p. 166 - 177.
lowland rice - nutrient management - measured values - growth-model - validation - benefits - balance - systems - urea - asia
In Jiangsu province, Southeast China, high irrigated rice yields (6-8000 kg ha(-1)) are supported by high nitrogen (N) fertilizer inputs (260-300 kg N ha(-1)) and low fertilizer N use efficiencies (recoveries of 30-35%). Improvement of fertilizer N use efficiency can increase farmers' profitability and reduce negative environmental externalities. This paper combines field experimentation with simulation modeling to explore N fertilizer management strategies to realize high yields, while increasing N use efficiency. The rice growth model ORYZA2000 was parameterized and evaluated using data from field experiments carried out in Nanjing, China. ORYZA2000 satisfactorily simulated yield, crop biomass and crop N dynamics, and the model was applied to explore options for different N-fertilizer management regimes, at low and high levels of indigenous soil N supply, using 43 years of historical weather data. On average, yields of around 10-11,000 kg ha(-1) were realized (simulated and in field experiments) with fertilizer N rates of around 200 kg ha'. Higher fertilizer doses did not result in substantially higher yields, except under very favorable weather conditions when yields exceeding 13,000 kg ha(-1) were calculated. At fertilizer rates of 150-200 kg ha(-1), and at the tested indigenous soil N supplies of 0.6-0.9 kg ha(-1) day(-1), high fertilizer N recovery (53-56%), partial N productivity (50-70 kg kg(-1)) and agronomic N use efficiency (20-30 kg kg(-1)) were obtained with application in three equal splits at transplanting, panicle initiation and booting. Increasing the number of splits to six did not further increase yield or improve any of the N use efficiency parameters. (c) 2006 Elsevier B.V. All rights reserved.
Effects of integrated control measures on earthworms, leaf litter and Venturia inaequalis infection in two European apple orchards
Holb, I.J. ; Heijne, B. ; Jeger, M.J. - \ 2006
Agriculture, Ecosystems and Environment 114 (2006)2-4. - ISSN 0167-8809 - p. 287 - 295.
fungicide use - scab - disease - urea - wint - netherlands - populations - management - ascospores - inoculum
Two-, three-year studies were conducted to determine the effect of combining chemical (fungicide and urea) and non-chemical (leaf shredding) sanitation treatments on earthworm populations, leaf litter density (LLD), and leaf and fruit infections caused by Venturia inaequalis in Dutch and Hungarian integrated apple orchards from 2000 to 2002 and 2001 to 2003, respectively. The combined sanitation treatment included urea and captan sprays applied to the tree and to the orchard floor and the shredding of fallen leaves in the previous autumn and winter. The earthworm numbers were significantly higher in the sanitation treatment compared to the treatment without sanitation in 2001 and 2002 (P <0.05) at Randwijk (The Netherlands) and in 2002 and 2003 (P <0.05) at Derecske (Hungary). LLD decreased continuously from leaf fall in late autumn to mid-May the following spring at Randwijk, which was explained well by a linear function fitted to the LLD data, with R 2 values ranging from 0.82 to 0.99. Model coefficients for the sanitation plots were significantly different (P <0.05) from those of the non-sanitized plots in 2001 and 2002. At Derecske, LLD started to clearly decrease in both treatments from February 2001 and 2002 and from March 2003 to late spring, and this was explained well by an exponential function fitted to the LLD data, with R 2 values ranging from 0.80 to 0.97. Model coefficients for the sanitation plots were significantly different (P <0.05) from those of the non-sanitized plots only in 2002. In most years and at both sites, the sanitation treatment resulted in significantly lower (P <0.05) scab incidence on spur-leaf clusters compared to the treatment without sanitation. However, the sanitation effect on scab levels on older leaves and fruits was low and varied by year and location. The results are discussed in connection with the environmental conditions in the two countries.
Check title to add to marked list
<< previous | next >>

Show 20 50 100 records per page

Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.