Development of sexual and agonistic behaviour in bulls and steers

Abstract

Traditionally in Britain, most male beef calves have been castrated. It is now becoming more common to rear entire males, but there is concern that sexual behaviour among bulls, particularly mounting, may be economically damaging, and that there may be aggression both between bulls and against stockmen. In this study, the development of sexual and agonistic behaviour in stable groups of Friesian--Holste in bulls and steers is compared. Twelve bulls and 12 steers, subjects of a growth trial, were studied. They were held in an open-sided house at 5 m:/calf, with ad libitum hay, concentrates and water. From 5 months old, each individual was observed for 1 h each month. All sexual, agonistic and affiliative interactions involving the focal individual were recorded, and mounting in the rest of the group was also noted. At 6.5 months, the pen was divided into halves, separating the bulls and steers. Preliminary results, up to 8 months old, are reported. Social interactions were frequent, with medians of 24/calf/h at 5--6 months and 12/ calf/h at 7--8 months after the groups were separated. There was a trend for bulls to be involved more than steers, but this was only significant at 7 months (medians 18.5 and 7, respectively). There were few differences between bulls and steers in the frequencies of particular types. Steers received more affiliative acts at 5 months, bulls gave and received more sexual acts at 7 months, but bulls and steers did not differ in frequency of agonistic interactions in any month. Agonistic interactions were infrequent, rarely severe, and often bi-directional in dyads, although there was some indication that the groups were developing rough hierarchies by 8 months. The clearest difference between the groups was in frequency of mounting. Bulls mounted more than steers in all months (medians 0.16--0.42 and 0--0.10/h, respectively). There was wide variation in this behaviour between different bulls, but individual frequencies of mounting were not consistent from month to month, and frequencies of being mounted only became consistent at 7--8 months. Most of the variation was attributable to short-term relationships in particular dyads, with one bull mounting another repeatedly over a period of from one to several days. Mounting among bulls tended to increase during the study, and could cause damage to some individuals.