Response from selection for income minus food cost in laying hens, estimated via the animal model

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Abstract
1. Selection for income minus food cost between 21 and 40 weeks of age was carried out in two replicate lines of brown egg layers for 5 generations in a population derived from a commercial cross between Rhode Island Red males and White Plymouth Rock females. Each replicate and an unselected control line consisted of 20 male and 80 female breeders. 2. Egg production, egg weight and food consumption were recorded on 1200 hens in every generation. Parent females were selected on individual performance. Males were not recorded and selected at random within half sib families to minimise rate of inbreeding. 3. A linear selection response of 0.46 and 0.43 monetary units per generation was observed, which resulted in a total response of 19.8% and 18.2% of the phenotypic mean of the base population over the 5 generations. A large increase in egg weight was the most important reason for the selection response in income minus food cost. 4. Further changes in associated traits were: an increase in egg number and egg mass, and a decrease in age at first egg, body weight and food: egg mass ratio. 5. The direct and correlated selection responses were similar in both lines. The realised response was somewhat less than expected in both lines. 6. A summary of phenotypic and genetic parameters, estimated from the data, is given. All genetic correlations between income minus food cost and the associated traits analysed, were in a favourable direction.