Response of the testes to social interaction among grouped chickens

Abstract

The effects of social interaction on the adaptive response of the testes were studied by maintaining chickens in experimental heterosexual groups for periods of 12 to 30 weeks. Increases in group size resulted in an increase in social conflict within groups. This interaction was reflected by smaller testes among the grouped males when compared with isolated and heterosexually paired cocks. The number of birds within a group rather than density seemed to be the important factor in determining the intensity of social interactions. Thus, in groups where sufficient space was allotted for freedom of movement, the frequency of interactions and decrease in testicular weight was as great as among groups of the same size where density made social contacts unavoidable. Within the groups testes weights were correlated with social rank. The most dominant males were found to have the heaviest testes while the subordinate cocks had the lightest and, occasionally, atrophic testes. The smaller testes associated with increased group size and subordinate social rank were attributed to degenerative changes in the germinal epithelium of grouped subordinate cocks. The most frequently encountered testicular changes were the formation of polynuclear giant cells and associated degenerative lesions within the germinal epithelium. In a few subordinate males complete regression was observed in the germinal layer of the testes. These observations support the hypotheses that social conflict may be an important factor in determining the adaptive response of the testes of chickens. Certain features of this response suggest that domestic fowl provide a useful species for further studies of reproductive function as related to their characteristic social interaction.