Genetic analysis of feather pecking behavior in laying hens

This thesis describes the genetic analysis of feather pecking behavior in laying hens. Feather pecking (FP) is a major welfare problem in laying hens.In the European Union, legislation concerning animal housing is becomingmore strict, because of increasing concern for animal welfare. Conventional cage systems will be banned in 2012 and there is a clear movement towards alternative housing systems such as modified cages and large group housing systems. Unfortunately, in large group housing systems FP is difficult to control. To study the genetics of FP behavior and open-field behavior, an F ₂ population of 630 hens coming from two commercial laying lines was generated. All F ₂ animals were tested for their FP behavior in a social FP test as well as for their behavior in an open-field test at both young and adult age. The F ₀ , F ₁ and F ₂ generations were genotyped with 180microsatellitemarkers. Gentle FP was heritable at both young and adult age whereas severe FP was not. Heritability of open-field behavior at young age was higher than at adult age.

A QTL analysis, using a half-sib model and a line-cross model was performed for different types of pecking behavior such as gentle FP, severe FP, aggressive pecking and toe pecking, as well as for receiving pecks and open-field behavior. For gentle FP suggestive QTL were identified at young age at GGA10 and at adult age at GGA2. In addition, for severe FP at adult age, a significant QTL was detected at GGA2. Parallel to this, using a comparative mapping approach, theglucocorticoidreceptor gene was mapped to GGA13. This chromosome was not detected in the QTL study which makes this gene less likely to be a candidate gene for FP behavior.

For receiving gentle FP, a significant QTL was detected on GGA1 at young age and at adult age a suggestive QTL was detected on GGA5. For open-field behavior atyoungage a significant QTL was detected on GGA4 and at adult age a significant QTL was detected on GGA4 as well. The QTL are more than 100cM apart, therefore, it is not likely that these QTL share the same underlying genes. Interestingly, these results indicate that pecking behavior as well as open-field behavior at young age is regulated by different genes than at adult age. The QTL for severe FP and gentle FP offer the possibility to identify genetic markers for FP behavior, which may be used in genetic improvement programs.