Feather pecking and aggressive pecking are recorded
by observation of the hens in defined time periods.
The observations are count values with large proportions of
zero counts. The latter one makes it difficult and in most
cases impossible to obtain a normal distribution by a data
transformation. The use of generalized linear mixed models
(GLMM) to analyze the data is an appropriate way to account
for the non-normal distribution of the data. In a recent
study we used dispersed Poisson models to estimate variance
components, heritabilities and approximate genetic
correlations for behavior traits in a large F2 cross of laying
hens (Bennewitz et al. (2014)). The aim of the present study
was to extent these analyses towards different observation
periods.