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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    Variants of the recently discovered avian gyrovirus 2 are detected in Southern Brazil and The Netherlands
    Santos, H.F. dos; Knak, M.B. ; Castro, F.L. de; Slongo, J. ; Ritterbusch, G.A. ; Klein, T.A.P. ; Esteves, P.A. ; Silva, A. Da; Trevisol, I.M. ; Claassen, E.A.W. ; Cornelissen, A.H.M. ; Lovato, M. ; Franco, A.C. ; Roehe, P.M. ; Rijsewijk, F.A.M. - \ 2012
    Veterinary Microbiology 155 (2012)2-4. - ISSN 0378-1135 - p. 230 - 236.
    chicken anemia virus - sequence alignment - disease virus - feathers - dna
    A genome of a virus preliminarily named avian gyrovirus 2 (AGV2), a close relative to chicken anemia virus, was recently discovered in a chicken in the state of Rio Grande do Sul, Southern Brazil. To study the occurrence of AGV2 in Rio Grande do Sul and the neighboring state Santa Catarina, a number of adult chickens (n = 108 and n = 48, respectively) were tested for the presence of AGV2 DNA. An AGV2-specific PCR was developed, optimized and used to analyze DNA extracted from clinical samples. AGV2 DNA was detected in 98/108 (90.7%) of samples collected in the state of Rio Grande do Sul and 29/48 (60.4%) of the samples collected in the state of Santa Catarina. In order to check whether AGV2 DNA would be detected in samples from a geographically distant region, DNA from brain samples of 21 diseased chickens from the Netherlands were tested independently, by the same method. In such specimens, 9/21 (42.9%) brain tissue samples were found to contain AVG2 DNA. Sequence analysis of some of the PCR products demonstrated that the amplified AGV2 sequences could vary up to 15.8% and could preliminarily be divided in three groups. This indicated the occurrence of variants of AGV2, which may reflect differences in geographical origin and/or in biological properties. The data presented here provides evidence that AGV2 seems fairly distributed in chickens in Southern Brazil and that AGV2 also circulates in the Netherlands. Besides, circulating viruses display genetic variants whose significance should be further examined, particularly to determine whether AGV2 would play any role in chicken diseases.
    Relevance of hair and spines of the European hedgehog (Erinaceus europaeus) as biomonitoring tissues for arsenic and metals in relation to blood
    Vermeulen, F. ; Havé, H. D'; Mubiana, V.K. ; Brink, N.W. van den; Blust, R. ; Bervoets, L. ; Coen, W. De - \ 2009
    Science of the Total Environment 407 (2009)5. - ISSN 0048-9697 - p. 1775 - 1783.
    pollution exposure assessment - lead levels - cadmium - l. - feathers - copper - areas - cows
    Hair has been proven to be suitable for non-destructive and non-invasive exposure assessments in human and mammal populations. A previous study with European hedgehog (Erinaceus europaeus) showed that, for some metals, hair and spine metal concentrations were positively correlated to levels in liver, kidney and muscle. Although blood has been studied in a wide variety of species, the relationship between hair and blood metal concentrations has yet to be quantified in many mammalian species. Tissue concentrations from hedgehogs residing in a park with known metal pollution were compared with those from a reference park and correlations between contaminant levels in hair and blood, and spines and blood were studied. Moreover, the relative distribution of arsenic and metals in hair, spines and blood was determined. Elevated concentrations were found in hedgehogs residing in the polluted site for As (8.2 ¿g/g, 6.3 ¿g/g, 3.6 ¿g/ml), Cd (0.48 ¿g/g, 0.17 ¿g/g, 0.02 ¿g/ml) and Pb (7.6 ¿g/g, 7.3 ¿g/g, 54 ¿g/ml), in hair, spines and blood respectively. Positive correlations were identified for exposure levels between hair and blood as well as between spines and blood for three elements (As, Cd, and Pb), whereas a negative correlation was found between Cr concentrations in spines and blood. In conclusion, hair and spines can be used to monitor blood concentrations of some metals, although more data are needed on uptake from the food chain and on the incorporation dynamics of these contaminants.
    Transfer of heavy metals in the food chain earthworm Black-tailed godwit (Limosa limosa): Comparison of a polluted and a reference site in The Netherlands
    Roodbergen, M. ; Klok, C. ; Hout, A. van der - \ 2008
    Science of the Total Environment 406 (2008)3. - ISSN 0048-9697 - p. 407 - 412.
    eggs - feathers - birds - population - cadmium - wetland - molt - lead - soil
    The Black-tailed godwit (Limosa limosa) is a migratory wader that favours wet meadows for breeding. The species has a Red List status in The Netherlands, as it strongly declined in numbers since the 1960s. Intensification of agriculture and land use change resulting in habitat loss are considered major causes of this decline. In some areas the breeding habitat is contaminated with heavy metals. Adult godwits mainly feed on earthworms in the breeding season, which are known to accumulate heavy metals from the soil. In this paper we investigate the transfer of heavy metals from the soil to the Black-tailed godwit, which may have an additive negative effect on the viability of local populations. We measured heavy metal concentrations in soil, earthworms, and godwit eggs and feathers at a polluted and a reference site. The results suggest that Lead, Mercury and Cadmium are transferred from the soil to godwits even though the species spends only a few months in the breeding area during the year
    Feather pecking and feather loss
    Rodenburg, T.B. ; Koene, P. - \ 2004
    In: Welfare of the laying hen / Perry, G.C., Wallingford, Oxfordshire, England : CABI (Poultry science symposium series 27) - ISBN 9780851998138 - p. 227 - 238.
    hennen - dierenwelzijn - diergedrag - verenpikken - veren (vogel) - verenkleed - hens - animal welfare - animal behaviour - feather pecking - feathers - plumage
    Characterizing feather peckers seems a viable approach towards a better understanding of the problem of feather pecking. With our current state of knowledge on the causation of feather peckinq, the environmental factors that influence the development of feather pecking and the characteristics of feather peckers and non-feather peckers, it should be possible to achieve more control over the problem of feather pecking in European flocks
    Geen effecten van alternatieve voeders : proef met veerkwaliteit opfokvleeskuikenouderdieren
    Emous, R.A. van; Harn, J. van - \ 2003
    De Pluimveehouderij 33 (2003)46. - ISSN 0166-8250 - p. 12 - 13.
    pluimveevoeding - voersamenstelling - beschadigingen - verenkleed - veren (vogel) - diervoedering - vleeskuikenouderdieren - poultry feeding - feed formulation - injuries - plumage - feathers - animal feeding - broiler breeders
    Het Praktijkonderzoek van de Animal Sciences Group van Wageningen UR heeft een kortlopend onderzoek (van 0-10 weken leeftijd) gedaan naar het effect van verschillende gehaltes in het voer op de kwaliteit van het verenkleed bij opfokvleeskuikenouderdieren.
    Ecotoxicological suitability of floodplain habitats in the Netherlands for the little owl (Athene noctua vidalli)
    Brink, N.W. van den; Groen, N.M. ; Jonge, J. de; Bosveld, A.T.C. - \ 2003
    Environmental Pollution (2003)1. - ISSN 0269-7491 - p. 127 - 134.
    terns sterna-hirundo - polychlorinated-biphenyls - lumbricus-terrestris - metal contamination - eisenia-foetida - heavy-metal - toxicity - feathers - organochlorine - accumulation
    This study describes the actual risks of exposure to contaminants, which little owls (Athene noctua vidalli) face in Dutch river floodplains. The results indicate that PCBs pose a risk: not only are levels in little owls from floodplains higher than levels found in little owls from a reference site but the PCB patterns in owls from the floodplains also indicate induction of hepatic cytochrome P450 enzymes by dioxin like compounds, possibly PCBs. Of the heavy metals, only cadmium is thought to pose a risk in certain conditions, for example, when little owls are feeding only on earthworms over a prolonged period of time. The results do not indicate any effects on the occurrence of prey items of the little owl like for instance earthworm, beetles and shrews. Hence, it is not expected that little owls will be affected by diminishing prey availability due to contamination.
    Vleeskuikenouderdieren: meer huidbeschadigingen bij onbehandelde hanentenen
    Haar, J. van der; Middelkoop, J.H. van - \ 2001
    De Pluimveehouderij 31 (2001)20. - ISSN 0166-8250 - p. 16 - 17.
    pluimveehouderij - hanen - tenen - afknippen - beschadigingen - hennen - huid - veren (vogel) - dierenwelzijn - vleeskuikenouderdieren - poultry farming - cocks - digits - clipping - injuries - hens - skin - feathers - animal welfare - broiler breeders
    Onderzoek van het Spelderholt toont aan dat het achterwege laten van de teenbehandeling bij de hanen extra huid- en veerbeschadigingen en extra verwondingen oplevert bij de hennen
    Achterwege laten van snavel- en teenbehandeling : niet zonder nadeel
    Haar, J.W. van der; Middelkoop, J.H. van - \ 2000
    De Pluimveehouderij 30 (2000)24. - ISSN 0166-8250 - p. 9 - 11.
    pluimveehouderij - dierenwelzijn - snavelkappen - hanen - afknippen - tenen - ovipositie - hennen - diergedrag - verenpikken - veren (vogel) - vleeskuikenouderdieren - poultry farming - animal welfare - debeaking - cocks - clipping - digits - oviposition - hens - animal behaviour - feather pecking - feathers - broiler breeders
    Door een deel van de achterste teen bij de hanen niet te verwijderen en de snavels van de hennen en hanen niet te behandelen nam de veerbeschadiging bij hennen toe. Bij de hennen met onbehandelde snavels was de broedeiproductie lager
    Veer- en huidbeschadigingen door het achterwege laten van ingrepen bij vleeskuikenouderdieren
    Haar, J.W. van der; Voorst, A. van - \ 2000
    Praktijkonderzoek voor de Pluimveehouderij 11 (2000)1. - ISSN 0924-9087 - p. 27 - 32.
    hennen - kippen - huidziekten - veren (vogel) - schade - vleeskuikenouderdieren - dierverzorging - hens - fowls - skin diseases - feathers - damage - broiler breeders - care of animals
    Bij het Praktijkonderzoek Pluimveehouderij (PP) 'Het Spelderholt' is bij vleeskuiken-ouderdieren onderzocht of het achterwege laten van ingrepen effect had op de veer- en huidbeschadigingen. De onderzochte ingrepen waren het afknippen van een deel vande achterste teen bij de hanen en de snavelbehandeling bij de hennen en de hanen. Door deze ingrepen achterwege te laten, ontstonden meer veer- en huidbeschadigingen bij de hennen.
    Verenopbrengst vleeseenden moeilijk te beinvloeden : proef met verrijkt voer, onbeperkt badwater en extra stro
    Buisonje, F.E. de; Enting, H. ; Wemmers, A. - \ 1999
    De Pluimveehouderij 29 (1999)31. - ISSN 0166-8250 - p. 18 - 19.
    eenden - vleesproductie - voedersupplementen - drinken - drinkwater - ligstro - veren (vogel) - productiviteit - rentabiliteit - ducks - meat production - feed supplements - drinking - drinking water - litter - feathers - productivity - profitability
    De verenopbrengst is van belang voor de rentabiliteit van de eendenhouderij. Om die reden is onderzocht of verrijkt voer, onbeberkt open water en tweemaal daags bijstrooien meer grammen aan veren oplevert
    Voldoet de strooiselbak? Onderzoek naar de hoeveelheid vet in de veren
    Rooijen, J. van; Niekerk, T.G.C.M. van; Reuvekamp, B.F.J. - \ 1995
    De Pluimveehouderij 25 (1995)28. - ISSN 0166-8250 - p. 11 - 11.
    ligstro - hennen - dierenwelzijn - huisvesting, dieren - veren (vogel) - pluimvee - vetweefsel - litter - hens - animal welfare - animal housing - feathers - poultry - adipose tissue
    Onderzoek naar de effectiviteit van een strooiselbak in welzijnkooien voor leghennen. De hoeveelheid vet in de veren kan een aanwijzing geven
    Stofbaden in welzijnskooien
    Rooijen, J. van - \ 1994
    Praktijkonderzoek voor de Pluimveehouderij 5 (1994)3. - ISSN 0924-9087 - p. 12 - 15.
    diergedrag - kooien - veren (vogel) - hennen - ligstro - pluimveehokken - bezettingsdichtheid - animal behaviour - cages - feathers - hens - litter - poultry housing - stocking density
    In het onderzoek naar alternatieve huisvesting voor leghennen (project 1030) worden o.a. welzijnskooien met strooiselbak onderzocht. Doel van het gedragsonderzoek binnen dit project is om te vast te stellen in hoeverre deze strooiselbakken voldoen.
    Soort verlichting van weinig invloed op bevedering vleeseenden
    Buisonjé, F.E. de - \ 1994
    Praktijkonderzoek voor de Pluimveehouderij 5 (1994)1. - ISSN 0924-9087 - p. 41 - 43.
    huisvesting, dieren - vogels - eenden - veren (vogel) - belichting - licht - verlichting - pluimvee - animal housing - birds - ducks - feathers - illumination - light - lighting - poultry
    Een toenemend probleem bij binnenhuisvesting van vleeseenden is de soms slechte bevedering waardoor op de slachterij verhoogde percentages B-kwaliteit kunnen voorkomen.
    Function and organization of dustbathing in laying hens
    Liere, D.W. van - \ 1991
    Agricultural University. Promotor(en): P.R. Wiepkema. - S.l. : S.n. - 123
    diergedrag - hennen - voortplanting - veren (vogel) - animal behaviour - hens - reproduction - feathers
    Dustbathing in laying hens ( Gallus gallus domesticus ) serves to remove excessive feather lipids which accumulate and become stale during dust deprivation. In addition and probably as a consequence of lipid removal the fluffiness of the downy feather parts is enhanced. A dustbath consists of appetitive tossings and consummatory rubbings. Its function as well as its organization depend on the nature of the bathing litter. The uninterrupted performance of rubbing is crucial and predicts consistent bathing litter preferences. An increase in stale feather lipids enhances the tendency to bathe, while sham-dustbathing occurs during dust deprivation. However, during long-term deprivation sham-dustbathing develops abnormally. This seems due to intrinsic reinforcement. Long-term deprivation of functional stimulation prescribed by phylogenetical standards may result in an uncontrollable motivation to dustbathe.

    The development and causation of feather pecking in the domestic fowl
    Blokhuis, H.J. - \ 1989
    Agricultural University. Promotor(en): P.R. Wiepkema. - S.l. : Blokhuis - 109
    pluimvee - kippen - diergedrag - huisvesting, dieren - veren (vogel) - ? - poultry - fowls - animal behaviour - animal welfare - animal housing - feathers

    Feather pecking in poultry consists of pecking directed at the feathers of other birds, sometimes pulling out and eating these feathers. It may result in severe damage of the integument of the birds, including wounds of the skin. Finally wounded birds may be pecked to death (cannibalism). About 30 years ago, when most poultry was kept in traditional floor systems, this behaviour was an important cause of mortality. Nowadays most birds are housed in small groups in battery cages in modern poultry houses and in The Netherlands they are usually beaktrimmed (partial amputation of the beak). This resulted somehow in a decreased mortality due to feather pecking.

    However, the effects of feather pecking may have become less fatal, the behaviour as such did not decrease and pecking still causes a lot of (feather) damage and feather pecking is still a problem in modern poultry farming.

    Firstly, the problem relates to animal welfare, which is clearly at stake for the pecked birds. Moreover, beaktrimming may counteract the occurrence of cannibalism and may prevent a lot of suffering, it is a painful operation which should be omitted if possible.

    Secondly, feather pecking is also economically detremental. Defeathering has a pronounced increasing effect on heat production, leading to an estimated increase of energetic needs between 5 and 20 % for laying hens in battery cages.

    The development and expected practical use of alternative systems for laying hens is also relevant with respect to feather pecking. As these systems often incorporate characteristics of traditional floor systems, this may enhance feather pecking.

    The present study was aimed at elucidating the basic motivation behind feather pecking and the process leading to it.

    In Chapter 2 pecking behaviour of birds on a litter floor was compared with that of birds on a slatted floor, from hatching until 17 weeks of age. The average frequency (per animal per hour) of pecking at conspecifics was 73.2 in groups on slatted floors and 27.8 in groups on litter. It increased over time in groups on slatted floors, whereas it tended to decrease in groups on litter floors. Moreover, in the latter pecking at conspecifics was much less damaging. Here about 20 % of the pecks was directed at particles on the plumage of other birds, which is relatively harmless, and about 25 % at feathers. In the groups without litter, these percentages were 1 and 55 respectively.

    Ground pecking frequency appeared to be about 6 times higher in groups on litter compared to groups on a slatted floor.

    At 17 weeks of age the experiment was continued by transferring half of the animals from each floor-type to the other type of flooring material. Most striking was that animals reared on litter and changed to slats, showed a strong increase of pecking at conspecifics (together with an increase in feather damage) and a strong decrease of ground pecking. Birds reared on slats and moved to litter showed a strong increase in ground pecking and the majority showed a decrease of pecking at conspecifics. In the latter birds, plumage recovered from the damage done to it in the first part of the experiment.

    It was concluded that the results supported the hypothesis that feather pecking evolves as redirected ground pecking.

    Experimental evidence to support this hypothesis is presented in Chapters 3 and 4. In Chapter 3 the motivation for groundpecking was experimentally varied in 6 week old female chicks, housed on litter. The same experimental procedure that stimulated ground pecking in chicks on a litter floor, appeared to stimulate feather pecking in chicks on a slatted floor. This supports the hypothesis that ground pecking and feather pecking share common causal factors. Chapter 4 takes another approach to test the same hypothesis. Here, again using 6 week old chicks, floor-type was suddenly changed from a half litter half slatted floor into a full slatted floor. The fact that groundpecking decreased and feather pecking increased again supported the above hypothesis.

    The redirection of ground pecking was described in both chapters in terms of incentive motivation theory. In this concept of motivation the role of incentive stimuli in inducing motivational states and in directing behaviour is emphasized. Specific characteristics of litter, a slatted floor or feathers which may affect their ranking as an incentive are discussed. Possibly visual, tactile or gustatory feedback signals play a role, as well as positive long-term effects of ingestion. Moreover, it was stated that the possibility to perform specific consummatory behaviour patterns, may also affect the validation of a substrate as an incentive. In relation to this it was also suggested that the possibility to perform groundscratching in combination with pecking, may add to the stimulus feedback. Obviously the animal's past experience with environmental stimuli is crucial in the validation of stimuli as incentive.

    In Chapter 5 the effects of early experience with litter were studied. Hens were reared on litter floors (20 groups) or on wire floors (20 groups) until 17 weeks of age. Then all groups were moved to pens with half litter half slatted floors. It appeared that feather pecking was less in litter reared hens compared to hens reared on wire. Also feather damage was less in the litter reared groups. It was concluded that experiences during rearing influence pecking preferences during the laying period.

    In the same experiment the effect of beaktrimming was studied. As the beak of the chicken has a variety of sensory receptors, beaktrimming is likely to result in sensory deficits. This may affect tactile discrimination and interfere with the validation of an object as an incentive for pecking. During the rearing period beaktrimmed birds showed a lower frequency of ground pecking as well as feather pecking, on litter as well as wire floors. During the laying period all groups showed the same level of ground pecking irrespective of beaktrimming or floor type. Beaktrimming only showed an effect on feather pecking in the wire reared groups. Here feather pecking reached a very high level, although it did not much harm to the plumage of the birds. It was concluded that beak trimming does not change pecking preference nor does it decrease pecking frequency. Beaktrimming is effective in reducing feather pecking damage.

    In Chapter 6, it is reported that a high housing density significantly decreases ground pecking and scratching in young domestic fowl. Although no serious feather pecking occurred, it is suggested that a high housing density stimulates the redirection of ground pecking which may result in the development of feather pecking.

    In the general discussion (Chapter 7) a regulatory model of ground pecking is presented, in which the role of incentives is incorporated. The motivation of pecking is discussed and it is concluded that pecking serves several functions such as energy supply, consummatory stimulation or information gathering. The model of ground pecking is modified to allow the incorporation of these different functions. On the basis of this model some suggestions for future research are made. In a last paragraph the risk of some husbandry factors in relation to the occurrence of feather pecking are discussed and some measures to prevent feather pecking are suggested.

    Feather meal : evaluation of the effect of processing conditions by chemical and chick assays
    Papadopoulos, M.C. - \ 1984
    Landbouwhogeschool Wageningen. Promotor(en): E.H. Ketelaars. - Wageningen : Papadopoulos - 139
    mest - veren (vogel) - pluimvee - voer van dierlijke oorsprong - manures - feathers - poultry - feed of animal origin
    Feather waste at poultry processing plants, has been of interest in nutritional studies because of its high protein content. This material must be hydrolyzed in order to be digested by the animal, because in its natural state it is of no nutritive value. However, this product will be of variable quality because hydrolysis has not only beneficial effects but can also reduce the nutritive value in terms of amino acid content and digestibility. Although feather meal is used in poultry feeding, our present knowledge of its protein-amino acid quality is inadequate. The value of feather meal as a component of animal feeds could be better assessed if more were known about the effect of different processing conditions on the content and digestibility of its amino acids. Therefore, the investigation described in this thesis was conducted in order to study chemical, nutritional and physiological aspects of feather meal treated under different conditions.

    The first major part of this study was an evaluation of feather meal proteinamino acid quality by chemical methods (Chapter 2). Crude protein analysis and digestibility determinations in vitro are often used in practice as a rapid quality-control method. The amino acid composition in relation to the amino acid requirements of the animal is also taken into account in formulating rations.
    The effects of five processing times (30, 40, 50, 60 and 70 min), five moisture contents (50, 55, 60, 65 and 70%), five added levels of sodium hydroxide (0.2, 0.3, 0.4, 0.5 and 0.6%) and proteolytic enzyme (0.2, 0.3, 0.4, 0.5 and 0.6%) upon amino acid concentration and nitrogen solubility of feather meal were studied by multiple regression techniques in three experiments (section 2.3.2). The first experiment examined the combinations of time and moisture. The second and third experiments contained the combinations of time, moisture, sodium hydroxide and of time, moisture, enzyme respectively. All test products were autoclaved at a constant temperature of 146°C.
    The results of these experiments showed that the individual amino acids have distinct variations in their response to various processing variables (time, moisture, sodium hydroxide, enzyme). There are losses, in qeneral, of amino acids during the processing of feather meal. These losses were more pronounced in the chemically treated feather meals, followed by the enzymatically treated ones compared with feather meals treated without additions. In the last treatments some amino acids, valine, leucine, tyrosine and phenylalanine, proved to be rather stable during processing. The protein solubility of the test
    feather meals in pepsin-HCl solution and alkali or acid solvents was increased as a result of processing. However, the amino acid contents and especially that of cystine were decreased. This suggests that the amount of cystine may be a reliable index of the degree of processing since feather meals with lower cystine content showed higher protein solubility/digestibility values.
    The reduction of amino acids can be explained by changes in the protein structure as a result of protein cross-linking reactions and the formation of new amino acids (section 2.5.3). Evidence of the nature of these chemical changes is given in section 2.4.5 in which the formation of the unnatural amino acid lanthionine concurrent with the drastic destruction of cystine is described.
    Summarizing the above, it can be concluded that:
    a) there is, in general, a negative processing effect on amino acid contents and a positive one on nitrogen solubility;
    b) amino acids and nitrogen solubility/digestibility, estimated by chemical methods, have very clear variations in their response to different process variables, leading to the conclusion that it is difficult to find an adequate criterion of optimal processing conditions;
    c) there is an inverse relationship between amino acid contents and nitrogen solubility/digestibility, suggesting that, in this stage, it is difficult to evaluate the effect of processing on feather meal protein as a whole from the corresponding effects on the amino acid contents and nitrogen solubility.

    The losses of amino acids as demonstrated in Chapter 2 may not be of much nutritional significance unless other structural modifications to the protein affect in vivo digestibility of crude protein and amino acids. There is a need for a bioassay of the protein because physico- chemical analyses have a limited value in that they give little or no indication of individual amino acid availability for digestion, absorption and metabolism by the animal. Therefore, a second major objective of this study was the use of biological methods for estimating the value of the differently processed feather meals (Chapter 3). In this chapter the effect of three processing times (30, 50 and 70 min) and three methods of treatments (without additions, added sodium hydroxide 0.4% and added enzyme 0.4%) were investigated. The digestibility of the test feather meal protein/amino acids was determined by quantitative excreta collection over a period of 36 hrs. All the test chicks were force- fed with 12 9 of feather meal (dry matter) given in 2 doses with a 3 hr interval between feeds. Correction was made for metabolic plus endogenous excretions by using a nitrogenfree diet to distinguish apparent from true digestibility.
    The apparent and true digestibility of all individual amino acids were influenced by the processing conditions. The main significant effect was the processing time. There was a negative time-linear effect on the digestibility of all amino acids of the feather meals, with the exception of leucine. Significant differences in digestibility coefficients due to the method of treatment were found for some amino acids, cystine, tyrosine, phenylalanine, serine and alanine. Their values were lower in the chemically treated feather meals. Comparison between the three methods of feather meal treatment revealed higher values for the enzymatically treated samples and lower values for the chemically treated ones, compared with samples treated without additions.
    An interesting feature of this experiment was the considerable variation between individual amino acids in their digestibility values. They ranged in apparent digestibility values from 22.5% for lysine to 82.4% for isoleucine and, in true digestibility values, from 36.3% for aspartic acid to 86.5% for isoleucine. The three limiting essential amino acids lysine, histidine and methionine, in increasing order, were particularly low in digestibility.
    The reduction in amino acid digestibility can be explained by the fact that autoclaving feather meal may have altered the protein structure in such a way that the enzymic attack, necessarily associated with the digestion process, is hindered. It has been suggested that heat/alkali causes the formation of new cross-linkages within the protein molecules and this leads to the formation of new amino acids (section 2.5.3), as in the case of lanthionine in our experiments. Cross-linkage formation reduces the rate of protein digestion possibly by preventing enzyme penetration or by blocking the sites of enzyme attack (section 3.5.3). Our results showed that feather meals with higher lanthionine content had lower amino acid digestibility values.
    Comparing the digestibility values of amino acids with those of crude protein, it appeared that the latter revealed differences between the differently processed feather meals which were not shown by the former. Furthermore, we found negative correlations between in vivo and in vitro tests.
    The following general conclusions may be drawn from this experiment:
    a) processing can affect amino acid digestibility of feather meal indicating that prolonged time (longer than 30 min) and use of NaOH are not desirable; a study on the effect of shorter than 30 min processing periods would be of interest;
    b) crude protein digestibility estimations cannot be used as predictors of amino acid digestibility;
    c) laboratory (in vitro) tests are not reliable in detecting inferior protein/amino acid quality in differently processed feather meals;
    d) the variations between individual amino acids in their digestibility values are sufficiently extensive to suggest that, in the formulation of diets for poultry, it is essential that the dietary feather meal protein must be balanced on the basis of digested amino acids;
    e) the lanthionine present in test feather meals may be a reasonable indicator of treatment damage since the amino acid digestibility values of processed feather meals are inversely proportional to the lanthionine contents of the test samples.

    The digestibility of the individual amino acids in dietary feather meal has also been studied in broiler chicks by their changes in the intestinal contents (Chapter 4) and blood plasma (Chapter 5). In these nutritional-physiological studies the feather meals prepared in Chapter 3 were also used. The test feeds were given to the birds by force-feeding in 3 equal doses at 3 hr intervals, to insure an adequate and controlled intake and to get a uniform distribution of the passage of feed. Nitrogen-free diet, standard amino acid mixture and casein were used as reference diets. Intestinal amino acid concentrations in jejunal and ileal contents of chicks Were measured at 21 hrs after the last force-feeding. These concentrations reflected the relative digestion of dietary feather meal protein as affected by different processing conditions. Digesta taken from the jejunum showed higher levels of amino acids derived from the chemically treated feather meals and lower levels from the enzymatically treated ones. The variations between intestinal amino acid levels were more pronounced in ileal digesta, where samples derived from feather meals processed for 30 min showed the lower amino acid levels. This was true for feather meals treated with enzymes and for products without additions, while the chemically treated feather meals showed an inverse trend. It should be noticed that feather meals treated for 30 min and the enzymatically treated products had the higher amino acid digestibility values while the chemically treated products were less well digested (Chapter 3).
    Comparing the ileal digesta derived from chicks fed on nitrogen-free diet and standard amino acid mixture, there were differences in the proportions of meth ionine, leucine, tyrosine, histidine and proline. Comparing the ileal digesta with the excreta, there were very close similarities in the proportions of all individual amino acids, with the exception of cystine, indicating an insignificant microbial influence on amino acids in the large intestine.
    It can be concluded that:
    a) the composition of a nitrogen-free diet may influence the amount of endogenous amino acids. These findings in relation to the small differences between apparent and true amino acid digestibility values found in this study (Chapter 3), suggest that apparent digestibility determinations are reliable measures for practical purposes;
    b) the similarity of the proportions of amino acids in the ileal digesta and excreta derived from the test feather meals, as well as from the nitrogen free diet, indicates that digestibility values for feather meal amino acids based upon fecal analysis are not substantially different from those obtained by using ileal assays. Comparative studies of ileal and fecal amino acid digestibility may be needed in order to prove the validity of the very close similarity of ileal and excreta amino acid composition. It is
    suggested, how ever, that fecal analysis is a more practical and reliable criterion for routine amino acid digestibility determinations, from the point of view of applied nutrition.

    Plasma amino acid concentrations in broiler chicks were estimated at 1 hr after the last force-feeding. There was a relationship between plasma amino acid levels and the relative digestibility of the feather meal protein subjected to various processing treatments. Comparisons between dietary/digested amino acids and their levels in plasma revealed significant correlations for the essential but not for the non-essential ones. Possible reasons for the lack of a precise relationship between dietary/digested and plasma amino acids are discussed in section 5.5.
    It can be concluded that:
    - although blood plasma studies may provide useful information on the relative digestion of dietary feather meal, it seems difficult to interpret plasma amino acid changes as a practical quantitative measurement of amino acid digestibility.
    The final conclusion, referring to the points of investigation which are mentioned in the introductory chapter is that:
    a) Feather meal protein-amino acids are affected in both their contents and digestibility, by different processing conditions, time being the most significant one.
    b) Chemical methods (total amino acids, soluble nitrogen) and qualitative assays in blood plasma and intestinal amino acids are not adequate to evaluate feather meal protein quality as affected by different processing conditions.
    c) Feather meal must be evaluated by quantitative in vivo digestibility measurements of the individual amino acids and should be used in poultry rations on the basis of the digested amino acids it supplies.

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