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Feather Pecking and Tryptophan Metabolism in Laying Hens

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Title: Feather Pecking and Tryptophan Metabolism in Laying Hens
Author: Birkl, Patrick
Department: Department of Animal Biosciences
Program: Animal and Poultry Science
Advisor: Harlander, Alexandra
Abstract: Feather pecking (FP) in laying hens is one of the greatest welfare issues in the husbandry of chickens kept for egg-laying. FP may result in severe feather damage or cannibalism, which can increase flock mortality. FP behaviour, mostly described as gentle or severe, is affected by multiple internal and external factors, but the biological mechanisms that regulate the development and continuation of FP are poorly understood. While tryptophan (TRP) metabolism has been hypothesized to impact FP, nutritional manipulation of plasma TRP using acute tryptophan depletion (ATD) for studying changes in pecking behaviour in a social and non-social environment has not been explored, to the best of our knowledge. Further, the influence of the social environment on the plasma TRP metabolism, along the kynurenine (KYN) pathway and FP, has not been considered. To manipulate TRP metabolism, we developed a nutritional, non-invasive ATD treatment for laying hens. The effect of ATD on gentle and severe FP in a social environment, as well as on pecking in an operant chamber, was evaluated. Disrupting social structures was utilized to observe any alterations in gentle and severe FP, and blood TRP metabolites along the KYN pathway. The results of this thesis indicate that ATD in laying hens reduces plasma TRP levels and increases pecking activity in a social (gentle FP) and non-social (operant pecking) environment. Furthermore, disrupting social structures has been found to lower KYN/TRP ratios and increase the likelihood of FP (gentle and severe merged). These findings indicate that even acute TRP metabolism-manipulation may impact pecking behaviour, and that the KYN pathway of TRP metabolism could help broaden our understanding of the biological mechanisms behind FP.
Date: 2020-02-01
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