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Term Organizing Effects of Prenatal Exposure to Testosterone Or Corticosterone on Feather Pecking

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Term Organizing Effects of Prenatal Exposure to Testosterone Or Corticosterone on Feather Pecking Long-term organizing effects of prenatal exposure to testosterone or corticosterone on feather pecking Mirjam Bakker Supervisor: Bernd Riedstra Minor Thesis Master Biology University of Groningen Abstract Even though feather pecking is a major problem in the poultry industry the mechanisms causing this behaviour are still unclear. One hypothesis considers FP as a part of normal social behaviour, several factors influencing social behaviour could therefore also influence FP. Firstly this could be preen wax composition since several studies have shown the importance of preen wax in individual recognition. Secondly maternal hormone deposition could affect social behaviour since exposure to these hormones can have long-lasting effects on the physiology and behaviour of the offspring. Two potentially interesting hormones are testosterone (T) and corticosterone (C) because both hormones have effects on social behaviour. We predict that increased prenatal exposure to T increases FP. Increased exposure to C could either increase or decrease FP; since previous studies show contradictory results for especially the stress pathways. In this study, eggs from laying hens were exposed to either T or C. 21 weeks after hatching chickens were housed inside in groups of 3 (1 treated female, 1 control female, 1 control male) and pecking behaviour was observed. Furthermore, biometry, comb characteristics and preen wax composition were determined. The stress response was determined with a tonic immobility test. Results show that testosterone had a direct effect on feather pecking; increased prenatal exposure to T resulted in more FP. Furthermore, testosterone had an indirect effect on FP by influencing preen wax. Corticosterone had no effect on feather pecking, but this study does confirm the effect of stress and dominance on FP. In conclusion it may be profitable to select parental strains for low yolk testosterone or otherwise monitor yolk T levels of eggs. This could reduce FP or warn for a higher risk on the development of feather pecking occurring in chicks bred from high yolk T level eggs. Introduction A major problem in the poultry industry is feather pecking (FP). These are pecks directed towards feathers of another individual. Two types of FP can be distinguished, gentle (GFP) and severe (SFP) pecking. Although GFP normally doesn’t result in substantial damage, very frequent pecking at the feathers deteriorates plumage quality. SFP is more problematic due to the pulling out of feathers. This can result in wounds, cannibalism and even death (van Horne & Achterbosch 2008; Serdaroğlu et al. 2013; Rodenburg et al. 2013). Due to feather pecking, i.e. egg weight is reduced and food intake increased. Therefore, next to decreased welfare, FP also causes economic losses (Chow & Hogan 2005; de Haas et al. 2013). Current methods to decrease the effects of injurious pecking are housing in reduced light conditions and beak trimming. Both methods bring along their own (welfare) problems: the former method impairs proper eye development (Siopes et al. 1984), the latter results in chronic pain due to damage to the nerves (Breward & Gentle 1985; Gentle et al. 1990; Quartarone et al. 2012). To increase welfare, beak trimming will be banned in the Netherlands from 2018 onwards. However, chickens with an intact beak can cause more damage to conspecifics, making it important to find a solution to this problem. Understanding the principles and mechanisms underlying the development of this behaviour are an important step in the search for a solution to prevent this behaviour in the future. There are several hypotheses explaining why feather pecking develops. Firstly, it is considered as redirected ground pecking behaviour. In nature chickens spent on average 60% of their time on foraging behaviour (Dawkins 1989). In the intensive poultry housing systems the nutritional demands are met in just a fraction of that time, whereas the ‘need’ to perform foraging behaviour remains high. Blokhuis & Arkes (1984) showed feather pecking probably develops from the need to perform foraging behaviour. Chickens living on a floor without substrate showed a higher FP frequency compared to chickens with substrate. However, learning where to peck at an early age does not seem to prevent FP in later life: de Jong et al. (2013) showed that feather pecking could not be prevented by raising chicks in a condition with plenty of adequate foraging material. Secondly, it could be that feather pecking develops due to a lack of suitable substrate to dust bathe. Dust bathing is a primary need for birds and Vestergaard & Lisborg (1993) showed that chickens with a substrate unsuitable for dust bathing pecked more towards conspecifics, compared to chickens with a suitable substrate. This fits with Blokhuis & Arkes (1984), although they argue that it’s a lack of foraging that causes FP, not a lack of dust bathing. Thirdly, feather pecking could develop due to a lack of specific nutrients. McKeegan & Savory (2001) found that chickens showing high FP frequency also ate more feathers. When fed more nutritional food, feather pecking declined (Savory et al. 1999). On the other hand, van Krimpen et al. (2005) showed that when chickens had to work harder for their food without changing nutritional value, FP also declined. Finally, feather pecking could also be part of normal social behaviour. Riedstra & Groothuis (2002) showed that chicks pecked more towards unfamiliar individuals at such early age that it was very unlikely that the behaviour was already redirected. It could be that FP is used to identify individuals and maintain social bonds and rank order (Harrison 1965). This can explain why it is often a dominant chicken pecking towards a subordinate and why the receiver often ignores gentle pecks. Furthermore, it is known that light induced lateralization (LiL) influences social behaviour. Light reaching the embryo in the egg in the later stages of incubation lateralizes brain and behaviour. Riedstra & Groothuis (2004) showed that LiL also influenced feather pecking early in life. Light incubated animals showed increased feather pecking behaviour and where less discriminating between familiar and unfamiliar chicks than dark incubated animals. Riedstra & Groothuis (2002) also noticed that severe pecking is initially accompanied by gentle pecking. They therefore argued that both are governed by the same motivational system, but that severe pecking is an escalated version of gentle pecking. This escalation could be due to stressful environments. In poultry farming, chickens are housed in large groups. This increases the demand for social exploration, because of the large number of unfamiliar birds surrounding an individual. The amount of unfamiliar birds is thought to be stressful for chickens. It is argued that SFP arises as a mechanism to cope with this (stressful) situation (Riedstra & Groothuis 2002). It could be that different coping styles (the way an individual reacts to certain events) can explain why not every chicken shows FP (Koolhaas et al. 1999). If feather pecking indeed is a social behaviour, it is probable that different kinds of cues that affect social behaviour are also involved in feather pecking. One such cue is individual recognition by olfaction. Recently it has become clear that olfaction is important in social behaviour and individual recognition in birds (for a review see Caro & Balthazart, 2010). An important source for olfactory signals is the preen gland (uropygial gland) located at the base of the tail feathers. This gland produces preen wax, which is used to coat feathers as part of plumage maintenance. Identification of preen wax showed that there are species and gender differences (Mardon et al. 2010; Biester et al. 2012) and also individual differences (Karlsson et al. 2010). Balthazart & Schoffeniels (1979) found that after removal of the preen gland, sexual displays are reduced, suggesting that the preen gland plays a role in mating (Johansson & Jones 2007; Hirao et al. 2009). Amo et al. (2012) showed starlings could discriminate sex of conspecifics by only using chemical cues. Chemical analyses of preen wax showed that there were sex and age differences. Going even further, Whittaker et al. (2013) found a correlation between wax composition and reproductive success, suggesting that preen wax could be used for mate choice. Sandilands et al. (2004) found that preen wax composition differed between pecked and non-pecked chickens, but only in one out of two experiments. Considering these findings, it is very probable that the preen gland is involved in social recognition in chickens and it could be possible that preen wax is a factor regulating feather pecking behaviour. Avian eggs contain many hormones of maternal origin. Maternal hormones could influence social behaviour. It is often argued that, to increase fitness in offspring, mothers can adjust the phenotype by changing the amount of hormones she deposits (for a review see Groothuis et al., 2005). In relation to feather pecking, both testosterone (T) and corticosterone (C) are potentially interesting. Increased prenatal exposure to T affects important traits, like aggression and growth (Rubolini et al. 2005; von Engelhardt et al. 2006) and could also effect dominance by influencing comb colour (Casagrande et al. 2012; Riedstra et al. 2013). Moreover Riedstra (2003) showed that hens from a high FP (HP) line had higher T levels than the low FP (LP) line. Lateralization affects FP, as mentioned above. Both T and C have been shown to reduce LiL, at least when administered to the egg late during incubation and in pharmacological doses (Riedstra & Groothuis 2004; Rogers & Deng 2005; Freire et al. 2006). It is unknown whether C and T override the effects of LiL applied at the onset of incubation in a physiological dose. Riedstra et al. (2013) showed a near significant effect for T, for C this is unknown. An alternative pathway for testosterone or corticosterone to affect FP behaviour is via a stress related mechanism. Stress is frequently implicated in inducing the development of feather pecking behaviour.
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