Comparison of Two Estrous Synchronization Protocols on Reproductive Performance of Dairy Cows

Lactating dairy cows (n=53) were used to evaluate the effect of two estrous synchronization protocols starting between d 10-12 of the estrous cycle on reproductive performance. Cows in the Ovsynch (Control) treatment (n = 24) received an i.m. injection of 10?g Gonadotropin Releasing Hormone (GnRH) agonist (Buserelin, Receptal®), followed 7 d later by an i.m. injection of 25 mg Prostaglandin F2? (PGF2?) and 48 h later by a second i.m. injection of 10?g GnRH. The protocol was concluded with the timed artificial insemination (TAI) 16-20 h after the second GnRH. Cows in the Short-ES estrous Synchronization treatment (Short-ES; n = 29) received an i.m. injection of 25 mg PGF2? and an i.m. injection of 1 mg estradiol benzoate (EB) dissolved in oil and 10?g GnRH 48 and 60 h after PGF2?, respectively. These cows were inseminated artificially at detected estrus. Blood samples were collected from all cows at days 0 (day of AI), 7, 14, 21, 22, and 23 after AI to determine P4 concentrations. Pregnancy rates from first AI were based on plasma P4 concentrations on d 22±1 post AI, and confirmed by rectal palpation between days 45 and 50 post AI. Results showed that more (P 0.01) cows in the Short-ES group (86.2%) exhibited estrus than in the Ovsynch group (41.7%). Pregnancy rates to first AI were greater (P 0.05) in the Short-ES group (37.4%) than in the Ovsynch (12.5%) group. In contrast, pregnancy losses were lower (P 0.05) in the Short-ES group (38.9%) than in the Ovsynch (76.9%) group. Pregnancy rates to second, third, and overall pregnancy rates were similar between both groups and between primiparous and multiparous cows. Days open for pregnant cows tended to be higher (P 0.09) in the Ovsynch group than in the Short-ES group. Plasma P4 concentrations were similar between pregnant and nonpregnant cows on days 0 and 7 after AI, however, were greater (P 0.01) for pregnant than nonpregnant cows on days 14, 21, 22, and 23 after AI. Results indicate that Short-ES protocol improves reproductive performance by increasing the number of cows exhibiting estrus and pregnancy rates to first AI compared with Ovsynch protocol.