Exposure of beef females to the biostimulatory effects of bulls with or without deposition of seminal plasma prior to AI

The objective of this experiment was to evaluate the biostimulatory effect of bull exposure, with or without the deposition of seminal plasma, on expression of estrus and pregnancy rate to AI in cattle. Beef heifers (n = 86) and cows (n = 193) were allocated to one of three treatments: (1) no bull exposure (CON; n = 95), (2) exposure to a bull with a surgically-deviated penis for 21 d prior to AI (DB; n = 88), or (3) exposure to a vasectomized bull for 21 d prior to AI (VB; n = 96). The DB treatment provided the physical presence of a bull but prevented intromission, whereas the VB treatment allowed for intromission and deposition of seminal plasma but not spermatozoa. The estrous cycles of all females were synchronized using the Select Synch + CIDR protocol (GnRH + CIDR-7 d-CIDR removal + PGF2α, detection of estrus + AI 12 h later for 84 h-clean-up TAI + GnRH). Pregnancy was detected via transrectal ultrasonography on d 35 post-AI. At the onset of the experiment, 75.7% of heifers and 86.1% of cows were estrous cycling. The percentages of females that displayed estrus were similar (P > 0.05) among treatments (71.4%, 76.8%, and 74.4% for CON, DB, and VB, respectively). Pregnancy rates tended to be greater (P = 0.06) in females in the DB treatment (60.5%) compared to females in the VB treatment (42.2%), with the control group intermediate (49.5%). In conclusion, biostimulation did not affect the expression of estrus but females exposed to the DB treatment tended to have an increased pregnancy rate.