Genetics of welfare: a comprehensive study of feather pecking in laying hens

Feather pecking is a serious problem in poultry production. It causes high economical losses and suffering in the affected birds. In spite of intensive research, the causes of this damaging behaviour are not fully understood. Genetic studies revealed sufficient genetic variation for selection against the damaging behaviour. However, feather pecking is a complex behaviour and more detailed information on the genetic background of the motivation is required to successfully implement this trait in breeding programmes. The prevailing hypothesis explains feather pecking as misdirected foraging behaviour, but other motivations, such as feather eating, aggression, fear and general locomotor activity may be involved. The interrelationships of feather pecking and the above mentioned behaviours have been studied using more than 900 birds of a F2-cross of two lines which have been selected for high and low feather pecking. Heritability, genetic and phenotypic correlations between the traits have been estimated using standard statistical models. In addition, Structural Equation Models (SEM) were applied to estimate putative causal relationships between feather pecking and other traits. Genetic correlation and Lambda coefficients showed a strong causal effect of feather eating and feather pecking. This supports the hypothesis that feather eating represents a primary cause of feather pecking. There was a substantial causal influence of aggression and general locomotor activity on feather pecking. Open-field activity (fear) and foraging in contrast did not show clear effects on feather pecking. Significant SNPs were identified for feather pecking and aggressive pecking in a genome-wide association study, using data of 817 birds of the F2-cross. Some of SNP clusters indicate relationships with physiological effects of monoamines, which are involved in the development of feather pecking and aggression. This information will be helpful in selection against the damaging behaviours in commercial layer lines.