Ph. D.

This dissertation consists of a series of four experiments designed to examine the interfacing of behavior, genetics, physiology and disease resistance in the domestic fowl. The principle objective was to obtain insights into the mechanisms involved in the responses of the domestic chicken to various husbandry situations. A second objective was to determine the degree of generalization of inferences which could be made to various populations of chickens that had different genetic backgrounds. Differences were found among various lines for "fear", head shaking, body weight and reproductive traits. In all cases the association of "fear" with head shaking was of a low magnitude and neither behavior had, on a within line basis, a significant relationship with growth and reproductive traits. A temporal effect which declined over time was noted for "fear" of humans by females maintained individually in cages suggesting habituation to such a husbandry situation. The effect of the sex-linked gene for dwarfing on the frequency of head shaking, antibody titers to sheep red blood cells, and plasma corticosterone levels was influenced by the genetic background of the population studied. Line differences were observed for the degree of mortality, lesions, and abnormal droppings in response to a challenge with E. coli. The disease and social history of the populations would, however, mask differences due to the particular genome of the population studied. Therefore, the response of a population of chickens to E. coli depends upon its genetic background, previous history, and the current husbandry situation. The stability of the social hierarchy after an E. coli challenge was influenced more by the degree of resistance of the individual to infection than by social inertia. The influence of short-term physical and social environmental changes were cumulative for traits such as antibody production, plasma corticosterone levels, plus changes in body weight, lymphocytes and heterophils. Lymphocytes were more responsive to the short term changes than heterophils. It appears from the data that "fear" and head shaking behaviors are vehicles by which chickens adapt to long term environmental changes, but are not used for short term adaptations. The data demonstrate specific relationships among the genome and mechanisms involved in the response of chickens to various husbandry situations. This implies that the adaptiveness of populations to various husbandry practices is greatly influenced by the genetic background of the specific population. The plasticity of populations, however, suggests that selection for various husbandry situations is feasible. / Ph. D.