Magnitude of Genetic Influence, Cage Type, and Genotype by Cage-Type Interactions on Soft-Shell and Shell-Less Egg Production

Genetic effects and the effects of single versus nine-bird colony cages upon the percent production of soft-shell (% SS), shell-less (% SL), and hard-shell (% HS) eggs were investigated in a randombred population of White Leghorns. Ovulation rate, (OR), % SL, and % HS eggs decreased (P<.01) in colony cages, while % SS eggs increased slightly (P<.01). It was concluded that crowding in the colony cage environment reduced OR. It was hypothesized that either demand for shell material was correspondingly reduced, or the number of double ovulations was reduced; both of which may result in a larger proportion of HS eggs. Significant sire effects (P<.05) and high heritabilities for % SS and % SL egg production were observed. A significant sire by cage environment (S × E) interaction was found for % SL but not for % SS or % HS egg production. However, the significant interaction for % SL was due to scale effect and not a reranking of sire means. A large positive genetic correlation of % SS eggs with % SL eggs was observed. The genetic correlations of % HS eggs with % SS or % SL eggs were small and not significantly different from zero in both environments. Possible physiological mechanisms were discussed.