Influence of the male effect on follicular dynamics and pregnancy rate in lactating cows undergoing fixed-time artificial insemination

The objective of this study was to determine the biostimulatory effect of bull exposure on follicular dynamic traits and pregnancy rate of lactating Nelore cows subjected to a fixed-time artificial insemination protocol. A total of 150 postpartum cows were randomly assigned to either a non-biostimulated or (C) and biostimulated (BS) group. Ovarian follicular dynamics was monitored by using transrectal ultrasonography. Females in both groups showed follicular regression after beginning the hormonal protocol. Daily follicular growth and percentage of ovulating females did not differ (P > 0.05) between groups. The interval between the start of the follicular wave and the ovulation was smaller (P < 0.05) in the C group; however, the pregnancy rate was greater (P < 0.05) in the B group. Furthermore, the BS group required less services per pregnancy (P < 0.05). In summary, the results allow to conclude that the association between the male effect and the Fixed Timed Artificial Insemination (FTAI), does increase the pregnancy rates and reduce the number of services per female, although there is no effect on follicular dynamics.