Influence of biostimulation on reproduction in postpartum beef cows.

Three experiments were conducted to evaluate the effects of biostimulation (exposure to bulls or androgenized females) on various reproductive variables in suckled beef cows. Bulls or testosterone-treated cows (TTC) were introduced to cows, randomly allotted to one of four groups, within 72 h postpartum. In Exp. 1, Groups 1 and 3 were exposed to bulls and Groups 2 and 4 were exposed to TTC. In Exp. 2, Groups 1 and 3 were exposed to bulls and Groups 2 and 4 served as controls (isolated from biostimulation). In Exp. 3, Groups 1 and 3 were exposed to TTC and Groups 2 and 4 served as controls. Mean postpartum intervals to estrus were not different between cows exposed to either bulls or TTC in Exp. 1 (P greater than .10). However, in Exp. 2 and 3, cows exposed to either bulls or TTC had reduced postpartum intervals to estrus (44 and 41 d, respectively) compared with control cows (52 d; P less than .05). Fewer control cows were in estrus at either 40 d (P less than .05; Exp. 2 and 3) or 60 d (P less than .05; Exp. 3) postpartum than were cows exposed to bulls or TTC. No differences were observed between groups in any experiment for postpartum intervals to pregnancy (P greater than .10). These data indicate that cows exposed to biostimulation from either bulls or TTC immediately after calving return to estrus earlier than do cows isolated from biostimulation.