Development of sexual behaviour in commercially-housed broiler breeders after mixing.

1. It has been reported that broiler breeder males behave aggressively towards females during mating. However, the cause of this aggressive sexual behaviour is not yet clear. In this experiment we studied the development of the sexual behaviour in male and female broiler breeders from mixing (20 weeks of age) until complete development of the behaviour (28 weeks of age) to formulate hypotheses on the causes of the aggressive mating behaviour. 2. Behaviour was observed on 8 farms with commercially-housed Ross 308 broiler breeder parent stock (males and females) at 20, 22, 24, 26 and 28 weeks of age, either observed by direct observations at 6 different locations in two units per farm, or recorded on video tape in one unit per farm for more detailed observations. 3. Broiler breeder males behaved aggressively towards females both during and outside the mating context. Some elements of courtship behaviour were not observed. Upon male approach hens either did not respond or they ran away. Males frequently used forced behaviour before mating (pushing hens into a crouch position). The majority of the matings did not succeed (no copulation, due to frequent escape of hens) and was forced (no voluntary crouching of the hen). Rough male behaviour did not decrease, neither did hens show habituation or a more "normal" response over the 8 weeks observation period. 4. We conclude that both male and female sexual behaviour of commercially-housed broiler breeders seem to be incomplete and may be indicative of poor welfare and stress, especially in the hens. We hypothesise that factors like separate rearing (common practice under commercial conditions), large group sizes and stocking density may play an important role in the development and performance of sexual behaviour and should be further studied.