発情回帰前の雌牛に対する雄牛の行動的関与

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The object is to study a possibility of the bull effect on resumption of estrous in cows from the viewpoint of behaviour. Two bulls grazing in each beef suckler herd, were conducted of follow-up study from sunrise to sunset for 112 hrs and 112.5 hrs, respectively. Maintenance behaviour and social behaviour of each focal bull were scored using the instantaneous sampling method and the focal animal sampling method, respectively. The results were: 1) Diurnal pattern of social behaviour corresponded with the diurnal pattern of grazing behaviour in bulls. 2) There was a difference between bulls in frequencies of social interaction. Reproductive performance is also different between bulls along with their behavioural performance. It suggests that there may be a difference in sexual ability between bulls in pasture mating. 3) Cows emitted very few social behaviours to bulls. It suggests that bulls' social behaviour may be more important than cows' social behaviour in social interaction between bulls and cows.4) Bulls emitted very few social behaviours to heifers and first calving cows except aggressive behaviour. There may be a less possibility of the male effect on heifers and first calving cows. 5) Bulls emitted significantly much social behaviours to older cows. 6) Cows immediately after calving received much social behaviours. These social behaviours increased quadratically with the elapsed days after calving. These suggest the existence of male effect on female reproductive physiology from the viewpoint of behavioural interactions between bulls and cows, especially older and newly calved cows.

発情回帰前の雌牛に対する雄牛の行動的関与

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