Effect of male-to-male aggressiveness and feed-restriction during rearing on sexual behaviour and aggressiveness towards females by male domestic fowl

This experiment was one part of a larger study investigating problems of aggression towards females by male broiler breeder fowl. To investigate causal mechanisms, we were interested in determining (1) if feed-restriction during rearing affects behaviour towards females at sexual maturity and (2) if aggressiveness towards females is correlated with general levels of aggressiveness. We compared broiler breeder males with commercial laying strain males, which were either fed ad libitum or were feed-restricted during the rearing phase, and with game strain males, bred for fighting. Differences in behaviour were determined by observing males during interactions with small groups of females. Laying strain males did not behave aggressively towards females, whether feed-restricted or fed ad libitum during rearing. Despite genetic selection for fighting ability, game strain males also were not aggressive towards females. Conversely, broiler breeder males displayed significantly higher levels of aggression towards females than did feed-restricted laying strain males (P<0.02). Broiler breeder males were rough with females during mating, whereas laying strain and game strain males were not. Females struggled more frequently during mating attempts by broiler breeder males (P<0.002) and interfered frequently when these males attempted to mate with other females. From our results, we conclude that (1) feed-restriction during rearing has little effect on the sexual and aggressive behaviour of laying strain males at maturity and (2) selection for aggressiveness has not resulted in males which are more aggressive to females. Aggression towards females appears to be a unique problem occurring in broiler breeder male strains and not a function of feed-restriction. (C) 2000 Elsevier Science B.V. All rights reserved.