Genetic analysis of strain differences in pre-laying behaviour in the fowl: an ethological and genetic analysis of differences in the pre-laying behaviour of two strains of domestic fowl (Gallus gallus domesticus) confined in battery cages: a study pertaining to the evolution and adaptiveness of behaviour under conditions of natural and artificial selection

Abstract

This thesis deals with the description and analysis of the pre-laying behaviour of two strains of domestic fowl (Gallus gallus domestlcus) in battery cages. Hens from one of these strains, known as the S line, showed stereotyped pacing behaviour before laying. Hens from the other strain, known as the T line, showed little or no pacing behaviour and tended to sit.Selection over two generations, for pacing in the S line and for sitting in the T line, consistently increased both variables: indicating genetic variation in the expression of the two traits.Crosses between the two lines, extending to backcross and Fl generations, indicated that the tendencies to pace and to sit during the pre-laying period were inherited separately. The tendency to sit appeared to be inherited additively, whereas the tendency topace (as opposed to not pacing) appeared to be inherited in adichotomous fashion, controlled by a single gene or a polygenic threshold system. Neither trait was sex-linked.It is suggested that the differences in the pre-laying behaviour of the two strains are due to differences in responsiveness to releasers for sitting behaviour. The T line generalise to sub-obtimal stimuli from the cage associated with the release of sitting behaviour; whilst the S line fail to do so,become frustrated, and in response to this frustration exhibit stereotyped pacing behaviour.The differences in the pre-laying behaviour of the two strains did not appear to be related to their responses to aversive stimuli or the frustration of feeding behaviour, or to their ability togeneralise to sub-optimal stimuli other than those associated with the release of sitting during the period before laying.Theoretical aspects of the study relelated to the genetics of behaviour and its evolution are relevant to Tinbergen's "derived" activities hypothesis, which postulates that some visual displays have been derived from the behaviour shown in response to motivational conflict or thwarting.Practical aspects of the study relate to the improvement of the welfare of domestic animals kept under intensive husbandry conditions by breeding domestic animals better adapted to life under such conditions than present day livestock.