PSV-B-15 Comparison of the 7-day Cosynch and 8-day Estradiol-Based Protocols for Synchronization of Ovulation and Timed Artificial Insemination in Suckled Bos Taurus Cows

The objective was to compare pregnancy rates (PR) on day 30 and pregnancy loss between days 30 and 60 (PL) after timed artificial insemination (TAI; day 0) using 2 synchronization protocols, and plasma progesterone on day 18 in suckled beef cows. Angus cows were randomly assigned to either 7-d progesterone CoSynch (7-d P + GnRH) or 8-d progesterone + estradiol (8-d P + ES) synchronization protocols for TAI. On day -10, cows in the 7-d P + GnRH treatment group (n=574) received a progesterone-releasing intravaginal device (PIVD) and GnRH, on day -3 the PIVD was removed and cows received cloprostenol. On day 0 (64 h after PIVD removal), cows received GnRH and were subjected to TAI. On Day -10, cows in the 8-d P + ES treatment group (n=574) received a PIVD and estradiol benzoate, on Day -2 the PIVD was removed, and cows received cloprostenol and estradiol cypionate. On day 0 (48 h after PIVD removal), cows were subjected to TAI. The TAI pregnancy rates for each treatment were determined on day 30 and day 60. In a subset of cows [n=81, (7-d P + GnRH, n=41; 8-d P + ES, n=40)], serum progesterone concentration was evaluated on day 18. The PR (7-d P + GnRH=48.9%; 8-d P + ES=45.6%) and PL (7-d P + GnRH=3.6%; 8-d P + ES=4.6%) did not differ (P≥0.28) between treatment groups. In a subset of cows, serum progesterone concentration on day 18 did not differ (P=0.67) between treatment groups but tended to be less (P=0.07) in cows that had PL compared with cows that had no PL. In conclusion, there was no difference in PR and PL between suckled beef cows using 7-d CoSynch or 8-d estradiol-based protocols for synchronization of ovulation and TAI.