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Genetic Parameters for Feather Pecking and aggressive Behavior in laying Hens using Poisson and linear Models
An F2-design was established from two selected laying hen lines, which included 910 F2-hens. Each pen was observed in 21 sessions of 20 min each, distributed over three consecutive days. An animal model was applied that treated the bouts observed within 20 minutes (short period) or the summed bouts within one day (medium period) as repeated observations. A dispersed Poisson distribution was assumed. Residual variance was approximated on the link scale by the delta method. The estimated variance components were on a similar level for the two observation periods, except the approximated residual variance. This was substantially smaller for the medium period, leading to lower heritabilities on the link scale for the short period compared to the medium period (0.11 vs. 0.19 for feather pecking and 0.09 vs. 0.24 for aggressive pecking). Variance components were also estimated using a linear model.
Keywords:
Feather pecking
Generalized linear model
Heritability
