Abstract
Relative performance levels were compared for White Leghorn pullets of a selected and an unselected control strain in different laying-house environments in each of two experiments. Experiment 1 involved single-bird cages, separated-strain flocks in floor pens, and intermingled-strain flocks in floor pens. In addition, Experiment 2 included a three-bird cage environment. Genotype by environment interactions were detected in Experiment 1 for egg and body weights and in Experiment 2 for rate of lay after sexual maturity, livability, egg weight, hen-housed rate of lay, egg mass, body weight, and body weight gain. Although fewer genotype by environment interactions were found in Experiment 1, there was a distinct tendency for the strains to differ (or fail to differ) in similar ways in each of the three environments compared in the two experiments.Pullets of the more aggressive and socially dominant selected strain were generally superior in performance to unselected strain pullets when they were intermingled in floor pens, but those differences tended to disappear when pullets of the two strains were kept in separated-strain flocks. These results are taken as indirect evidence supporting the conclusion that differences in stress associated with the social environment may contribute to genotype by housing environment interactions for performance traits.Selected strain pullets generally were superior to unselected strain pullets when kept in cages with unlimited feed available. Unselected strain pullets put on excessive weight in cages as indicated by both linear and curvilinear regression analyses; the lighter the pullets were in body weight the greater the number of eggs laid after 40 weeks old. However, under the same conditions, selected strain pullets were, on the average, near optimal body weight for maximum egg production during the latter part of the laying year.
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