Experiments were designed firstly to investigate whether selection for growth has modulated the development of aggressive behaviour in male broiler chicks, and secondly to determine the influence of feed restriction on aggression. In the first experiment, broiler males were compared with males from a brown egg-laying strain and a white egg-laying strain. No significant differences were found between brown and white egg-type males in the frequency of pecking and threatening, with both groups showing a rise in these behaviours as expected until 8 weeks of age. Pecking and threatening in broilers, however, remained extremely low throughout this period. Sparring did not differ among the three strains. In the second and third experiments, broilers fed either ad libitum (AD) or placed on skip-a-day feed restriction (SK) were compared. SK sparred less but were more aggressive than AD until 15 weeks of age. Aggressive activity in SK was particularly elevated on feed-off mornings, and decreased to its lowest levels after SK were placed on full feed for only 4 days. Selection for growth thus appears to have resulted in a decrease in aggressiveness, regardless of actual body weight, at least when food is provided ad libitum. It is concluded that problems associated with aggressive behaviour are likely to be of little significance in commercial broiler flocks, which are marketed at 7-8 weeks of age, but are of importance in breeder flocks maintained on feed-restricted diets.
|Publication Title||Applied Animal Behaviour Science|
|Author Address||Dep. Poultry Sci., Univ., College Park, MD 20742, USA.|
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