- Email: [email protected]
Laying Hens Learn to Avoid Feathers
Research Note Laying Hens Learn to Avoid Feathers A. Harlander-Matauschek,*1 F. Wassermann,* J. Zentek,† and W. Bessei* *Department of Farm Animal Ethology and Poultry Science, University of Hohenheim, 470c, 70599 Stuttgart, Germany; and †Institute of Nutrition, Faculty of Veterinary Medicine, Free University of Berlin, Brümmestr. 34, 14195 Berlin, Germany solution (S). The other 24 birds were kept as a control (C) without access to feathers. After a 10-d feather feeding period, 3 groups of 4 S and 4 C birds each and 3 groups of 4 Q and 4 C birds each were assembled. Feather-pecking behavior was recorded over a period of 8 d. The number of Q feathers eaten was significantly lower than the number of S feathers. Birds that were offered Q feathers in the feather feeding phase showed significantly less severe feather pecking than S and C birds. The results clearly show that Q as an unpalatable substance was the signal the animal used to avoid damaging the feather cover in laying hens.
Key words: laying hen, feather pecking, feather eating, feedback, taste aversion 2008 Poultry Science 87:1720–1724 doi:10.3382/ps.2007-00510
INTRODUCTION Feather pecking is characterized as nonaggressive pecking (Anderson et al., 2007). In its mildest form, it has been observed as gentle repeated pecks at the tips and edges of feathers without removal of the feather. In its severe form, it is a forceful pecking with pulling and feather removal, which causes feather damage and feather loss (Savory, 1995). Recent studies have shown that feather pecking is positively associated with feather eating (Harlander-Matauschek et al., 2006a, 2007a,b). The question arises if feather eating in laying hens is a consequence of a positive characteristic of feathers. Although feathers are considered to have almost no nutritive value (McCasland and Richardson, 1966), swallowed feathers increase feed passage time in feather-pecking birds (Harlander-Matauschek et al., 2006b) similar to insoluble fiber-rich diets (Krogdahl, 1986). It has also been found that increased fiber content in the food improved the feather cover of laying hens due to less feather pecking (Wahlström et al., 1998). Chickens are omnivores and eat a combination of plant and animal matter (Wood-Gush, 1971); they ©2008 Poultry Science Association Inc. Received December 17, 2007. Accepted April 16, 2008. 1 Corresponding author: [email protected]
swallow their food whole or with little oral manipulation. From this point of view, learning about the consequences of ingesting specific food may contribute substantially to diet selection in chickens. Herbivores learn to avoid harmful and prefer nutritious food through foraging (Provenza, 1995). Learning through foraging assumes that diet selection is a result of positive and negative consequences of foraging. Thus, animals consume a particular food, experience positive (nutrient award) or negative (malaise) effects, and adjust their preference for the ingested food on the basis of their postingestive experience (Provenza and Balph, 1990). The question arises if the preference for eating feathers is associated with positive or negative experience. So far no attention has been paid to the feedback mechanisms that relate to feather-pecking or feather-eating behavior, or both, in laying hens. In the present paper, we investigate if we can alter conditioned feather eating in laying hens when feathers are paired with palatable substances (positive feedback) and acquire aversion to feathers when paired with unpalatable substances (negative feedback). Second, we test if the aversively conditioned laying hens from the first part of the experiment avoid severe feather pecking in a group situation (severe pecking can result in feather plucking and eating). Finally, we test if positively conditioned laying hens show more feather pecking than their conspecifics.
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ABSTRACT Previous work demonstrated an association between feather pecking and feather eating in laying hens. This raised the question if digestive feedback affects feather eating or feather pecking in laying hens. We hypothesized that feathers enriched with sugar form a positive feedback and feathers enriched with quinine sulfate form a negative feedback. Forty-eight laying hens were kept in individual cages and fed a pelleted diet ad libitum. Twenty-four birds were offered feathers on a daily basis; 12 of these birds were offered feathers soaked in 4% quinine sulfate solution (Q), and the other 12 were offered feathers soaked in 4% sucrose
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RESEARCH NOTE
Conditioning Phase
Statistical Analysis
Forty-eight birds were divided into 3 groups: group Q = 12 birds with access to feathers soaked in 4% quinine sulfate solution (catalog no. 16371, Acros Organics BVBA, Geel, Belgium); group S = 12 birds with access to feathers soaked in 4% sucrose solution (Suedzucker AG, Mannheim, Germany); and group C = 24 birds with no access to feathers. To produce palatable (group S) and unpalatable feathers (group Q), we soaked 100 g of feathers in 1,000 mL of 4% sucrose solution or 4% quinine sulfate solution for 12 h, respectively. We then allowed feathers to dry for 12 h. These concentrations were chosen because they were known to generate either preference (sucrose solution, Gentle, 1972) or aversion (quinine sulfate solution, Gittleman et al., 1980) in domestic chicks. Over a period of 10 d, we tested the response of each bird to the presentation of palatable (group = S) and unpalatable (group = Q) feathers (~4 to 5 cm in length) plucked from dead White Leghorn birds. Ten feathers were put into a transparent piece of stiff plastic (10 × 8 cm), which was fixed next to the food once every morning (0900 h). The number of feathers pulled out of the plastic and found on the cage floors, in the feed troughs and in the drop pans, was counted 20 min after presenting the feathers. The number of feathers eaten was calculated by subtracting the sum of the feathers found by the number of feathers presented. The drop pans were cleaned before presenting the feathers on a daily basis.
Pecking Behavior in the Group After the conditioning phase, 3 groups of 4 S and 4 C birds each and 3 groups of 4 Q and 4 C birds each were randomly assembled and placed in furnished
The number of feathers eaten during the conditioning phase was analyzed as repeated measurement with a general linear mixed model (Piepho et al., 2003; Piepho, 2004). The model was fitted using PROC MIXED (SAS 9.1, SAS Institute, 1999) with feather treatment (Q, S) and run (10 d) as fixed effects and animal as a random effect. The feather treatment × run interaction was also included in the model. To meet the assumption of the mixed model, the homogeneity and normality of general linear mixed model residuals were also investigated. PROC GLIMMIX (SAS 9.1, SAS Institute, 1999) was used to analyze the number of severe and gentle feather-pecking bouts as a repeated measurement with feather treatment (Q, S, C), run (8 d), and compartment (S + C group and Q + C group) as fixed effects and animal as a random effect. The count data were modeled as a generalized linear mixed model with a Poisson distribution and a log link. The degrees of freedom were adjusted using the Kenward-Roger method. Data are presented as mean ± standard error.
RESULTS AND DISCUSSION In the conditioning phase, the average intake of S feathers was greater than the average intake of Q feathers (P < 0.0001; Figure 1). This notable preference for S feathers may be explained by palatability. Palatability is classically defined to be a function of the taste, odor, and surface characteristics of foods (Arnold, 1981). Palatability is best understood as a compound phenomenon emerging from the interrelationship between the chemical senses (taste, smell, surface) and positive or negative postingestive feedback (Provenza, 1995).
Downloaded from http://ps.oxfordjournals.org/ at University of Southern Queensland on June 23, 2015
The present study comprised 2 phases (conditioning and group-housing situation). A total of 48 Lohmann Brown laying hens were reared and kept in a deep litter system before the experimental situation. At 26 wk of age, birds were transferred to individual cages measuring 43 × 43 × 45 cm (length × width × height). The feed trough was placed at the front and a nipple drinker at the back of the cage. Each cage was supplemented with a perch of 20-cm length. The cages were separated by nontransparent boards so that the birds had no physical or visual contact to their neighbors. The hens were kept in a ventilated, windowless room at a constant temperature (20°C). Lights were on from 0400 until 1800 h. The Hohenheim University 17.2% CP, 11.1 MJ/kg pelleted layer ration and water were provided ad libitum in both phases of the experiment. The conditioning phase started after 1 wk of adaptation to the experimental situation.
cages (Aviplus, Big Dutchman International GmbH, Vechta, Germany). The cages measured 120 × 78 × 54 cm (length × width × height) and included a nest, litter box, and perches. Feather pecking was recorded over a period of 8 d. The first day was not included in the analysis. The hens of each cage were directly observed for 10 min once in the morning between 0800 and 1200 h and once in the afternoon between 1330 and 1630 h. Data from the morning and afternoon session were combined. All cages were observed in a randomized order as described in Anderson and Adams (1991). To exclude involuntary bias, the observer was unaware of which feather treatment the hens had in the conditioning phase. Birds were individually tagged. During the 10-min observation period, all occurrences of severe and gentle feather-pecking bouts (Savory, 1995) were recorded. Feather pecks successively directed at the same pen mate were recorded as 1 bout. A bout ended when there were no pecks during a period of 5 s.
MATERIALS AND METHODS
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Figure 2. Mean number + SE of severe and gentle feather pecking bouts in quinine sulfate, sucrose, and control birds in the grouphousing situation during 8 d of observation. a,bBars with different letters are significantly different (P < 0.05). Q = quinine sulfate; S = sucrose; C = control.
In this experiment, Q and S birds did not differ in feather intake during the first 2 d of conditioning (Figure 1). It has been shown that when a new type of food is introduced, animals will avoid eating the food for a period of time (Launchbaugh et al., 1997). Forbes and Shariatmadari (1994) reported that laying hens need a period of learning before becoming proficient in the selection of food components. These could be explanations for the results here, which may mean that the laying hens of the present experiment had to get familiar with the new feathers. After d 2, the number of S feathers eaten increased over the experimental period of 10 d, whereas Q feathers were avoided (feather treatment × day interaction, P < 0.001). Animals form strong preferences for foods and flavors based on positive feedback from nutrients such as energy and protein (Provenza, 1995; Villalba and Provenza, 1996, 1997). Gentle (1972) showed that 5% sucrose solutions were the only form of sugar for which birds showed a significant preference. Starlings also preferred food enriched with sugar in a study by Schuler (1983), who assumed that the birds were able to measure the energy gain postingestive. However, the birds may have preferred food containing sugar because of its sweet taste. The same could be true for the present experiment, in which it was clear that the laying hens learned to eat sweet feathers. Whether feathers were chosen due to the sweet taste or due to the resulting energy gain could not be distinguished in the present experiment. But it could be concluded that palatability, meaning the interrelationship between taste and energy gain, may play an important role in S feather-eating behavior. Conversely, Q feathers were avoided in the conditioning phase. Food aversion occurs when animals learn to avoid a particular food by relating its specific taste with nauseous feedback (Garcia and Holder, 1985). In chicks, it has been shown that Q solution generates
aversion (Gittleman et al., 1980). In an investigation by Skelhorn and Rowe (2006), chicks learned to avoid unpalatable 4% Q food crumbs. In the present study, the conditioning phase of Q hens appears to enhance bias against feathers, because feather eating was not shown. In the group-housing situation, Q birds showed almost no severe feather pecking. The Q birds showed a significantly lower number of severe feather-pecking bouts than C (P < 0.04) and S (P < 0.007) birds (Figure 2). The results clearly show that Q, an unpalatable substance, was the signal the animal used to avoid damaging the feather cover in laying hens in the group-housing situation. This may mean that the birds associated ingestion of Q feathers with aversive effects and learned to recognize feathers from conspecifics as the aversive item in the group-housing situation. Control and S birds did not differ in the number of severe feather-pecking bouts (Figure 2). Although C birds were deprived from feathers in the conditioning phase, it could be assumed that the C birds developed a demand for feathers. Before the birds were individually caged, C birds were chosen from group-housed birds, in which feather pecking, feather eating, or both was possible. It has been shown that birds prefer a reward – in the present experiment, a feather – with greater deprivation (Marsh et al., 2004). Although the cages were separated by physical and visual barriers, it cannot be excluded that C birds may have observed S birds eating feathers during the conditioning phase. Social learning influences the preferences of domestic hens for novel food (Sherwin et al., 2002). Additionally, there is evidence that feather pecking is transmitted through social learning (Zeltner et al., 2000). It could be assumed that social learning is involved in feather eating as well, due to the fact that feather eating is positively associated with feather pecking (Harlander-Matauschek and Bessei, 2005).
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Figure 1. Daily mean number + SE of quinine sulfate and sucrose feathers eaten over a period of 10 d during the conditioning phase. Q = quinine sulfate; S = sucrose.
RESEARCH NOTE
ACKNOWLEDGMENTS This work was supported by the German Research Foundation. A. Harlander gratefully acknowledges H. P. Piepho (University of Hohenheim, Germany) for statistical advice
REFERENCES Anderson, K. E., and A. W. Adams. 1991. Effects of type of cage front and feed trough partitions on productivity and ingestive, agonistic, and fearful behaviors of egg-type hens. Poult. Sci. 70:770–775. Anderson, K. E., D. R. Jones, G. S. Davis, and P. K. Jenkins. 2007. Effects of genetic selection on behavioral profiles of single comb White Leghorn hens through two production cycles. Poult. Sci. 86:1814–1820. Arnold, G. W. 1981. Grazing behaviour. Pages 79–104 in Grazing Animals. F. H. W. Morley, ed. Elsevier, Amsterdam, the Netherlands. Broom, D. M. 1981. Biology of Behaviour. Cambridge University Press, Cambridge, UK. Dixon, L. M., G. J. Mason, and I. J. H. Duncan. 2007. What’s in a peck? A comparison of the motor patterns involved in feather pecking, dustbathing and foraging. Page 47 in Proc. 41st Int. Congr. ISAE, Merida, Mexico. F. Galindo and L. Alvarez, ed. International Society of Applied Ethology, Merida, Mexico.
Forbes, J. M., and F. S. Shariatmadari. 1994. Diet selection for protein by poultry. World’s Poult. Sci. J. 50:7–24. Garcia, J., and M. D. Holder. 1985. Time, space and value. Hum. Neurobiol. 4:81–89. Gentle, M. J. 1972. Taste preference in the chicken (Gallus domesticus L.). Br. Poult. Sci. 13:141–155. Gittleman, J. L., P. H. Harvey, and P. J. Greenwood. 1980. The evolution of conspicuous coloration: Some experiments in bad taste. Anim. Behav. 28:897–899. Harlander-Matauschek, A., C. Baes, and W. Bessei. 2006a. The demand of laying hens for feathers and wood shavings. Appl. Anim. Behav. Sci. 101:102–110. Harlander-Matauschek, A., I. Benda, C. Lavetti, M. Djukic, and W. Bessei. 2007a. The relative preferences for wood shavings or feathers in high and low feather pecking birds. Appl. Anim. Behav. Sci. 107:78–87. Harlander-Matauschek, A., and W. Bessei. 2005. Feather eating and crop filling in laying hens. Arch. Geflugelkd. 69:241–244. Harlander-Matauschek, A., K. Häusler, and W. Bessei. 2007b. A note on the relative preferences of laying hens for feathers from different body parts. Appl. Anim. Behav. Sci. 108:186–190. Harlander-Matauschek, A., H. P. Piepho, and W. Bessei. 2006b. The effect of feather eating on feed passage in laying hens. Poult. Sci. 85:21–25. Krogdahl, A. 1986. Antinutrients affecting digestive functions and performance in poultry. Pages 239–248 in Proc. 7th Eur. Poult. Conf., Paris, France. World’s Poultry Science Association, French Branch, Tours, France. Launchbaugh, K. L., F. D. Provenza, and M. J. Werkmeister. 1997. Overcoming food neophobia in domestic ruminants through addition of a familiar flavour and repeated exposure to novel foods. Appl. Anim. Behav. Sci. 54:327–334. Marsh, B., C. Schuck-Paim, and A. Kacelnik. 2004. State dependent learning affects foraging choices in starlings. Behav. Ecol. 15:396–399. McCasland, W. E., and L. R. Richardson. 1966. Methods for determining the nutritive value of feather meals. Poult. Sci. 45:1231–1236. Piepho, H. P. 2004. An algorithm for a letter-based representation of all-pairwise comparisons. J. Comput. Graph. Statist. 13:456–466. Piepho, H. P., A. Büchse, and K. Emrich. 2003. A hitchhikers guide to the mixed model analysis of randomized experiments. J. Agron. Crop Sci. 189:310–322. Provenza, F. D. 1995. Postingestive feedback as an elementary determinant of food preferences and intake in ruminants. J. Range Manage. 48:2–17. Provenza, F. D., and D. F. Balph. 1990. Applicability of five diet-selection models to various foraging challenger ruminants encounter. Pages 423–460 in Behavioural Mechanisms of Food Selection, NATO ASI Series. Vol. G20. R. N. Hughes, ed. Springer Verlag, Berlin, Germany. SAS Institute. 1999. SAS/STAT Users Guide. Version 8. SAS Inst. Inc., Cary, NC. Savory, C. J. 1995. Feather pecking and cannibalism. World’s Poult. Sci. J. 51:215–219. Schuler, W. 1983. Responses to sugars and their behavioural mechanism in the starling. Behav. Ecol. Sociobiol. 13:243–251. Sherwin, C. M., C. M. Heyes, and C. J. Nicol. 2002. Social learning influences the preferences of domestic hens for novel food. Anim. Behav. 63:933–942. Skelhorn, J., and C. Rowe. 2006. Prey palatability influences predator learning and memory. Anim. Behav. 71:1111– 1118. Villalba, J. J., and F. D. Provenza. 1996. Preference for wheat straw by lambs conditioned with intraruminal infusions of sodium propinate. J. Anim. Sci. 74:2362–2368.
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Sucrose birds were conditioned with tasty sweet feathers and most likely expected sweet, palatable feathers in the group-housing situation. However, feathers from conspecifics were apparently not as palatable as during the conditioning phase. The conditioned S birds may not have been motivated strongly enough to severely peck and pluck conspecific feathers in the absence of S on the feathers. It is assumed that untreated feathers from conspecifics were not as rewarding as S feathers. However, the S treatment in the conditioning phase may not have been sustainable in the group-housing situation. Neither S nor Q treatments influenced the number of gentle feather-pecking bouts. A recent publication showed that gentle feather pecking, possibly allogrooming, arises from a motivation different to that of foraging, whereas severe feather pecking arises from the motivation to forage (Dixon et al., 2007). The fact that only severe feather pecking was influenced by Q treatment may give evidence that severe feather pecking derives from the motivation to forage. The aim of foraging is acquiring food (Broom, 1981), whereby the aim of severe feather pecking seems to be consuming feathers (A. Harlander-Matauschek and K. Häusler, University of Hohenheim, unpublished data). Severe feather pecking and feather eating were inhibited by Q in the present experiment. Neither the observation day nor the compartment influenced the number of severe or gentle feather-pecking bouts. In conclusion, the present experiment provided positive evidence for the role of palatability of feathers on feather-eating and feather-pecking behavior in laying hens.
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Villalba, J. J., and F. D. Provenza. 1997. Preference for flavoured foods by lambs conditioned with intraruminal administration of nitrogen. Br. J. Nutr. 78:545–561. Wahlström, A., R. Tauson, and K. Elwinger. 1998. Effects on plumage condition, health and mortality of dietary oats/ wheat ratios to three hybrids of laying hens in different housing systems. Acta Agric. Scand. 48:250–259.
Wood-Gush, D. G. M. 1971. The behaviour of the domestic fowl. Heinemann Educational Books Ltd., London, UK. Zeltner, E., T. Klein, and B. Huber-Eicher. 2000. Is there social transmission of feather pecking in groups of laying hen chicks? Anim. Behav. 60:211–216.
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Key words: laying hen, feather pecking, feather eating, feedback, taste aversion 2008 Poultry Science 87:1720–1724 doi:10.3382/ps.2007-00510
INTRODUCTION Feather pecking is characterized as nonaggressive pecking (Anderson et al., 2007). In its mildest form, it has been observed as gentle repeated pecks at the tips and edges of feathers without removal of the feather. In its severe form, it is a forceful pecking with pulling and feather removal, which causes feather damage and feather loss (Savory, 1995). Recent studies have shown that feather pecking is positively associated with feather eating (Harlander-Matauschek et al., 2006a, 2007a,b). The question arises if feather eating in laying hens is a consequence of a positive characteristic of feathers. Although feathers are considered to have almost no nutritive value (McCasland and Richardson, 1966), swallowed feathers increase feed passage time in feather-pecking birds (Harlander-Matauschek et al., 2006b) similar to insoluble fiber-rich diets (Krogdahl, 1986). It has also been found that increased fiber content in the food improved the feather cover of laying hens due to less feather pecking (Wahlström et al., 1998). Chickens are omnivores and eat a combination of plant and animal matter (Wood-Gush, 1971); they ©2008 Poultry Science Association Inc. Received December 17, 2007. Accepted April 16, 2008. 1 Corresponding author: [email protected]
swallow their food whole or with little oral manipulation. From this point of view, learning about the consequences of ingesting specific food may contribute substantially to diet selection in chickens. Herbivores learn to avoid harmful and prefer nutritious food through foraging (Provenza, 1995). Learning through foraging assumes that diet selection is a result of positive and negative consequences of foraging. Thus, animals consume a particular food, experience positive (nutrient award) or negative (malaise) effects, and adjust their preference for the ingested food on the basis of their postingestive experience (Provenza and Balph, 1990). The question arises if the preference for eating feathers is associated with positive or negative experience. So far no attention has been paid to the feedback mechanisms that relate to feather-pecking or feather-eating behavior, or both, in laying hens. In the present paper, we investigate if we can alter conditioned feather eating in laying hens when feathers are paired with palatable substances (positive feedback) and acquire aversion to feathers when paired with unpalatable substances (negative feedback). Second, we test if the aversively conditioned laying hens from the first part of the experiment avoid severe feather pecking in a group situation (severe pecking can result in feather plucking and eating). Finally, we test if positively conditioned laying hens show more feather pecking than their conspecifics.
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Downloaded from http://ps.oxfordjournals.org/ at University of Southern Queensland on June 23, 2015
ABSTRACT Previous work demonstrated an association between feather pecking and feather eating in laying hens. This raised the question if digestive feedback affects feather eating or feather pecking in laying hens. We hypothesized that feathers enriched with sugar form a positive feedback and feathers enriched with quinine sulfate form a negative feedback. Forty-eight laying hens were kept in individual cages and fed a pelleted diet ad libitum. Twenty-four birds were offered feathers on a daily basis; 12 of these birds were offered feathers soaked in 4% quinine sulfate solution (Q), and the other 12 were offered feathers soaked in 4% sucrose
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RESEARCH NOTE
Conditioning Phase
Statistical Analysis
Forty-eight birds were divided into 3 groups: group Q = 12 birds with access to feathers soaked in 4% quinine sulfate solution (catalog no. 16371, Acros Organics BVBA, Geel, Belgium); group S = 12 birds with access to feathers soaked in 4% sucrose solution (Suedzucker AG, Mannheim, Germany); and group C = 24 birds with no access to feathers. To produce palatable (group S) and unpalatable feathers (group Q), we soaked 100 g of feathers in 1,000 mL of 4% sucrose solution or 4% quinine sulfate solution for 12 h, respectively. We then allowed feathers to dry for 12 h. These concentrations were chosen because they were known to generate either preference (sucrose solution, Gentle, 1972) or aversion (quinine sulfate solution, Gittleman et al., 1980) in domestic chicks. Over a period of 10 d, we tested the response of each bird to the presentation of palatable (group = S) and unpalatable (group = Q) feathers (~4 to 5 cm in length) plucked from dead White Leghorn birds. Ten feathers were put into a transparent piece of stiff plastic (10 × 8 cm), which was fixed next to the food once every morning (0900 h). The number of feathers pulled out of the plastic and found on the cage floors, in the feed troughs and in the drop pans, was counted 20 min after presenting the feathers. The number of feathers eaten was calculated by subtracting the sum of the feathers found by the number of feathers presented. The drop pans were cleaned before presenting the feathers on a daily basis.
Pecking Behavior in the Group After the conditioning phase, 3 groups of 4 S and 4 C birds each and 3 groups of 4 Q and 4 C birds each were randomly assembled and placed in furnished
The number of feathers eaten during the conditioning phase was analyzed as repeated measurement with a general linear mixed model (Piepho et al., 2003; Piepho, 2004). The model was fitted using PROC MIXED (SAS 9.1, SAS Institute, 1999) with feather treatment (Q, S) and run (10 d) as fixed effects and animal as a random effect. The feather treatment × run interaction was also included in the model. To meet the assumption of the mixed model, the homogeneity and normality of general linear mixed model residuals were also investigated. PROC GLIMMIX (SAS 9.1, SAS Institute, 1999) was used to analyze the number of severe and gentle feather-pecking bouts as a repeated measurement with feather treatment (Q, S, C), run (8 d), and compartment (S + C group and Q + C group) as fixed effects and animal as a random effect. The count data were modeled as a generalized linear mixed model with a Poisson distribution and a log link. The degrees of freedom were adjusted using the Kenward-Roger method. Data are presented as mean ± standard error.
RESULTS AND DISCUSSION In the conditioning phase, the average intake of S feathers was greater than the average intake of Q feathers (P < 0.0001; Figure 1). This notable preference for S feathers may be explained by palatability. Palatability is classically defined to be a function of the taste, odor, and surface characteristics of foods (Arnold, 1981). Palatability is best understood as a compound phenomenon emerging from the interrelationship between the chemical senses (taste, smell, surface) and positive or negative postingestive feedback (Provenza, 1995).
Downloaded from http://ps.oxfordjournals.org/ at University of Southern Queensland on June 23, 2015
The present study comprised 2 phases (conditioning and group-housing situation). A total of 48 Lohmann Brown laying hens were reared and kept in a deep litter system before the experimental situation. At 26 wk of age, birds were transferred to individual cages measuring 43 × 43 × 45 cm (length × width × height). The feed trough was placed at the front and a nipple drinker at the back of the cage. Each cage was supplemented with a perch of 20-cm length. The cages were separated by nontransparent boards so that the birds had no physical or visual contact to their neighbors. The hens were kept in a ventilated, windowless room at a constant temperature (20°C). Lights were on from 0400 until 1800 h. The Hohenheim University 17.2% CP, 11.1 MJ/kg pelleted layer ration and water were provided ad libitum in both phases of the experiment. The conditioning phase started after 1 wk of adaptation to the experimental situation.
cages (Aviplus, Big Dutchman International GmbH, Vechta, Germany). The cages measured 120 × 78 × 54 cm (length × width × height) and included a nest, litter box, and perches. Feather pecking was recorded over a period of 8 d. The first day was not included in the analysis. The hens of each cage were directly observed for 10 min once in the morning between 0800 and 1200 h and once in the afternoon between 1330 and 1630 h. Data from the morning and afternoon session were combined. All cages were observed in a randomized order as described in Anderson and Adams (1991). To exclude involuntary bias, the observer was unaware of which feather treatment the hens had in the conditioning phase. Birds were individually tagged. During the 10-min observation period, all occurrences of severe and gentle feather-pecking bouts (Savory, 1995) were recorded. Feather pecks successively directed at the same pen mate were recorded as 1 bout. A bout ended when there were no pecks during a period of 5 s.
MATERIALS AND METHODS
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Figure 2. Mean number + SE of severe and gentle feather pecking bouts in quinine sulfate, sucrose, and control birds in the grouphousing situation during 8 d of observation. a,bBars with different letters are significantly different (P < 0.05). Q = quinine sulfate; S = sucrose; C = control.
In this experiment, Q and S birds did not differ in feather intake during the first 2 d of conditioning (Figure 1). It has been shown that when a new type of food is introduced, animals will avoid eating the food for a period of time (Launchbaugh et al., 1997). Forbes and Shariatmadari (1994) reported that laying hens need a period of learning before becoming proficient in the selection of food components. These could be explanations for the results here, which may mean that the laying hens of the present experiment had to get familiar with the new feathers. After d 2, the number of S feathers eaten increased over the experimental period of 10 d, whereas Q feathers were avoided (feather treatment × day interaction, P < 0.001). Animals form strong preferences for foods and flavors based on positive feedback from nutrients such as energy and protein (Provenza, 1995; Villalba and Provenza, 1996, 1997). Gentle (1972) showed that 5% sucrose solutions were the only form of sugar for which birds showed a significant preference. Starlings also preferred food enriched with sugar in a study by Schuler (1983), who assumed that the birds were able to measure the energy gain postingestive. However, the birds may have preferred food containing sugar because of its sweet taste. The same could be true for the present experiment, in which it was clear that the laying hens learned to eat sweet feathers. Whether feathers were chosen due to the sweet taste or due to the resulting energy gain could not be distinguished in the present experiment. But it could be concluded that palatability, meaning the interrelationship between taste and energy gain, may play an important role in S feather-eating behavior. Conversely, Q feathers were avoided in the conditioning phase. Food aversion occurs when animals learn to avoid a particular food by relating its specific taste with nauseous feedback (Garcia and Holder, 1985). In chicks, it has been shown that Q solution generates
aversion (Gittleman et al., 1980). In an investigation by Skelhorn and Rowe (2006), chicks learned to avoid unpalatable 4% Q food crumbs. In the present study, the conditioning phase of Q hens appears to enhance bias against feathers, because feather eating was not shown. In the group-housing situation, Q birds showed almost no severe feather pecking. The Q birds showed a significantly lower number of severe feather-pecking bouts than C (P < 0.04) and S (P < 0.007) birds (Figure 2). The results clearly show that Q, an unpalatable substance, was the signal the animal used to avoid damaging the feather cover in laying hens in the group-housing situation. This may mean that the birds associated ingestion of Q feathers with aversive effects and learned to recognize feathers from conspecifics as the aversive item in the group-housing situation. Control and S birds did not differ in the number of severe feather-pecking bouts (Figure 2). Although C birds were deprived from feathers in the conditioning phase, it could be assumed that the C birds developed a demand for feathers. Before the birds were individually caged, C birds were chosen from group-housed birds, in which feather pecking, feather eating, or both was possible. It has been shown that birds prefer a reward – in the present experiment, a feather – with greater deprivation (Marsh et al., 2004). Although the cages were separated by physical and visual barriers, it cannot be excluded that C birds may have observed S birds eating feathers during the conditioning phase. Social learning influences the preferences of domestic hens for novel food (Sherwin et al., 2002). Additionally, there is evidence that feather pecking is transmitted through social learning (Zeltner et al., 2000). It could be assumed that social learning is involved in feather eating as well, due to the fact that feather eating is positively associated with feather pecking (Harlander-Matauschek and Bessei, 2005).
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Figure 1. Daily mean number + SE of quinine sulfate and sucrose feathers eaten over a period of 10 d during the conditioning phase. Q = quinine sulfate; S = sucrose.
RESEARCH NOTE
ACKNOWLEDGMENTS This work was supported by the German Research Foundation. A. Harlander gratefully acknowledges H. P. Piepho (University of Hohenheim, Germany) for statistical advice
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Sucrose birds were conditioned with tasty sweet feathers and most likely expected sweet, palatable feathers in the group-housing situation. However, feathers from conspecifics were apparently not as palatable as during the conditioning phase. The conditioned S birds may not have been motivated strongly enough to severely peck and pluck conspecific feathers in the absence of S on the feathers. It is assumed that untreated feathers from conspecifics were not as rewarding as S feathers. However, the S treatment in the conditioning phase may not have been sustainable in the group-housing situation. Neither S nor Q treatments influenced the number of gentle feather-pecking bouts. A recent publication showed that gentle feather pecking, possibly allogrooming, arises from a motivation different to that of foraging, whereas severe feather pecking arises from the motivation to forage (Dixon et al., 2007). The fact that only severe feather pecking was influenced by Q treatment may give evidence that severe feather pecking derives from the motivation to forage. The aim of foraging is acquiring food (Broom, 1981), whereby the aim of severe feather pecking seems to be consuming feathers (A. Harlander-Matauschek and K. Häusler, University of Hohenheim, unpublished data). Severe feather pecking and feather eating were inhibited by Q in the present experiment. Neither the observation day nor the compartment influenced the number of severe or gentle feather-pecking bouts. In conclusion, the present experiment provided positive evidence for the role of palatability of feathers on feather-eating and feather-pecking behavior in laying hens.
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