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 ag gression towards females by male broiler breeder fowl. To investigate causa l mechanisms, we were interested in determining (1) if feed-restriction dur ing rearing affects behaviour towards females at sexual maturity and (2) if aggressiveness towards females is correlated with general levels of aggres siveness. We compared broiler breeder males with commercial laying strain m ales, which were either fed ad libitum or were feed-restricted during the r earing phase, and with game strain males, bred for fighting. Differences in behaviour were determined by observing males during interactions with smal l groups of females. Laying strain males did not behave aggressively towards females, whether fe ed-restricted or fed ad libitum during rearing. Despite genetic selection f or fighting ability, game strain males also were not aggressive towards fem ales. Conversely, broiler breeder males displayed significantly higher leve ls of aggression towards females than did feed-restricted laying strain mal es (P<0.02). Broiler breeder males were rough with females during mating, w hereas laying strain and game strain males were not. Females struggled more frequently during mating attempts by broiler breeder males (P<0.002) and i nterfered 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 t o be a unique problem occurring in broiler breeder male strains and not a f unction of feed-restriction. (C) 2000 Elsevier Science B.V. All rights rese rved.