Group Selection for Adaptation to Multiple-Hen Cages: Behavioral Responses ,

Abstract

Three stocks of White Leghorns were compared for behavioral traits when kept in single-bird (1H) and 12-hen (12H) layer-house cages. Genetic stocks consisted of a commercial strain (X), a randombred control (C), and a stock derived from C and selected on the basis of kin's group performance information for increased survival and egg production over seven generations (S). Experimental units consisted of four consecutive 1H cages or a single 12H cage. All birds within a unit had intact beaks and were of the same stock. Each stock was represented by hens in 48 units of both 1H and 12H cages, and by 48 males (C and S stocks only) in 1H cages. Birds that died were replaced. Observations involved hens in their home cages except for tonic immobility (TI) and pair contests.Observations carried out soon after birds were placed in layer-house cages indicated that avoidance of the observer was essentially absent after pullets were observed on the 1st and 2nd d. Behavioral profile frequencies differed for nearly all behaviors compared in 1H and 12H environments. Following initially high crouching and low feeding frequencies, apparently normal levels were present by Days 15 and 16 posthousing. During the initial adaptation phase, genetic stock differences were not found within 1H cages and were present in only 2 of 10 categories in 12H cages. Young adult profiles also indicated no differences among stocks in 1H cages, but stock differences were found in 6 of 12 categories in 12H cages. In those cases, X strain hens differed from hens of the C and S stocks, but C and S hens did not differ from each other. Comparisons carried out between hens in 1H and 12H cages revealed that fearfulness was greater in 12H cages.Genetic stock comparisons, involving relative fearfulness and feeding and movement in a frustrating situation indicated that the X stock frequently differed from both C and S, but C and S did not usually differ from each other. However, observations of hens’ agonistic activity in the 12H home cage environment revealed that the S stock had fewer agonistic acts than the C stock from which it was derived, and both C and S had less agonistic activity than the X stock. Pair contests carried out within and between C and S stocks in both sexes yielded results inconsistent with those for agonistic activity in 12H cages. The C and S hens did not differ, but S males were more aggressive and, in between-strain contests, were more dominant.