The effect of fenceline bull exposure on expression of oestrus in dairy cows

The objective of this study was to investigate whether dairy cows visit and interact with a fenceline-housed bull more during oestrus than outside oestrus and whether fenceline bull contact affects expression of oestrus. At one end of a free stall a fence with vertical open bars was placed behind which a bull could be housed, allowing interactions with the cows. A closed fence with two blinded entrances was placed before the fence, creating a contact area. The experiment consisted of three treatments; it started with the control treatment (no bull on the farm) and was followed by bull treatment (a bull housed behind the fence) and no bull treatment (a bull present on the farm but not housed behind the fence). Signs of oestrus were observed every 4 h for 30 min and cows were equipped with pedometers. On the day of oestrus, cows were more frequent in the contact area during the bull treatment (12.0 ± 9.8 times) and the no bull treatment (13.9 ± 10.2 times) than during the control treatment (2.6 ± 2.5 times). The frequency of visits to the contact area was low and not different between treatments on the other days (2.2 ± 1.9 times). More cows had direct contact with the bull on the day of oestrus (71.4%) compared to the days outside oestrus (21.4-30%). The duration of direct contact with the bull was highly variable between cows and did not differ between oestrus and non-oestrus days. Behaviour and duration of oestrus were not affected by treatment but the relative increase in number of steps during oestrus tended to be higher in the bull (5.5 ± 0.2) and no bull treatment (5.3 ± 0.3) than in the control treatment (4.6 ± 0.3). In conclusion, dairy cows in oestrus seem to be attracted by a bull or by the expectation of the presence of a bull, but fenceline bull exposure does not affect behavioural expression of oestrus.