Agonistic behaviour and feather pecking in single-sexed and mixed groups of laying hens

The effects of the presence of males on female aggressiveness and feather pecking in groups of about 500 laying hens housed in an aviary system were studied. In all, 10 groups of ISA Brown laying hens were observed at 21, 35, 45 and 55 weeks of age on two farms, during two years. In the second year, with the second batch of birds, the groups also contained 50% Shaver 288 white females. Half of the groups included one ISA Brown male per 20-27 females. Stocking densities varied from 14.7 to 17.2 animals per square meter. The results of direct observation of 25 randomly selected focal animals per group showed that aggressive behaviour (aggressive pecks, threats and fights) among females was significantly less frequent in groups that also included males; the mean incidence (+/-SE) for the four ages was per group for single-sexed groups: 10.1 +/- 1.8 and for mixed groups: 5.9 +/- 0.9 (P < 0.01). Agonistic behaviour (aggressive behaviour and avoidances) among females was 63% +/- 2 more frequent in single-sexed groups than among hens in mixed groups (P < 0.01). The males were seldom seen to show aggressive behaviour towards females or towards each other. For feather pecks, there were no significant differences between single-sexed and mixed groups. It was concluded that the presence of males had a reducing effect on agonistic behaviour, but not on feather pecking among female laying hens housed in large groups at high stocking densities. (C) 1999 Elsevier Science B.V. All rights reserved.