Male broiler breeder fowl display high levels of aggression toward females.

Commercial broiler breeder males are reported to display high levels of aggression, often injuring and sometimes killing females. Aggression toward females by mature male domestic fowl is rare and may be regarded as aberrant behavior. The objective of this study was to determine the effects of genetic strain and feed restriction on the sexual and aggressive behavior of male domestic fowl. A 3 x 2 factorial design was used to compare the behavior of three genetic strains (two broiler breeder strains and one commercial laying strain) on two feeding regimens (one restricted and one fed ad libitum) between 25 and 37 d of age. At 22 wk of age, pairs of same-strain males were penned with 20 females of a broiler breeder strain. Behavior was sampled from each pen for six 10-min periods during Weeks 25, 27, 29, 33, and 37. Broiler breeder males displayed significantly more male-to-male (P < 0.0197) and male-to-female aggression (P < 0.0005) than laying strain males. Broiler breeder males chased females (P < 0.0001), forced more copulations (P < 0.0003), and displayed little courtship behavior (P < 0.0001) compared with laying strain males. There were no behavioral differences between broiler breeder strains. It was expected that feed restriction would result in increased aggression. However, males fed ad libitum displayed the most male-to-male (P < 0.0035) and male-to-female (P < 0.0273) aggression. Sexual behavior was not affected by feeding regimen. In conclusion, broiler breeder males display aberrant sexual behavior and extremely high levels of aggression, which are associated with genetic differences, not feed restriction.