Influence of bull exposure on reproductive performance of postpartum dairy cows

Abstract

The biostimulation of exposure to a male can improve postpartum reproductive performance in females of many species. The aim of this research was to examine the biostimulatory effects of fenceline bull exposure during the early postpartum period in lactating dairy cows on the resumption of ovulatory activity, subsequent conception and calving interval, either in naturally cycling or oestrus syncronised cows. Three experiments were carried out in which Holstein-Friesian cows were allocated after parturition between two groups: cows that had unlimited time of access to fenceline bull exposure (BC) and a control group that was not exposed to a bull (NBC). Experiment 1, assessing the effects of bull exposure on cows at varied stages post partum, showed that the interval from start of exposure to resumption of ovarian activity, assessed by milk progesterone concentration, was not significantly affected by bull presence. Cows showed generally poor visible indicators of oestrus making correct insemination timing difficult consequently prolonged the calving interval. Experiment 2, investigating the biostimulation approach for freshly calved cows, showed an increase in pregnancy rate to the first service and consequent reduction in calving interval. This was especially marked in those cows previously treated with a progesterone intra-vaginal device (PRID). The average number of services per conception was lower in biostimulated cows, though there was no significant improvement of oestrus detection in these cows. Experiment 3, investigating cows that were freshly calved and then syncronised for oestrus using PRID treatment, showed a similar improvement in conception rate to first service, though compromised by generally poor reproductive performance. Similarly, oestrus detection rate was low even with PRID treatment. The outcomes from this study highlight the potential effects of a biostimulation approach as a strategy to improve reproductive performance in postpartum anoestrus dairy cows raised in intensive farming systems.