Production, Management and the Environment: Reproduction and Behavior

d before initiating treatments. Cows were blocked by lactation number and assigned randomly to 3 treatments consisting of variations of the Ovsynch protocol. Cows in Cosynch-48 and Ovsynch received injections of GnRH 7 d before and 48 h after a PGF injection. Fixed-time inseminations (TAI) were made at the time of the second GnRH injection (0 h; Cosynch-48) or 24 h (Ovsynch). Those in Cosynch-72 received the second GnRH injection at 72 h after PGF and were inseminated at the same time. Pregnancy was diagnosed by palpation on d 40 or 41 after TAI. Pregnancy rates in both herds were consistently greater (P < 0.05) for Cosynch-72 than for Cosynch-48 and Cosynch-72 vs. Cosynch-48 + Ovsynch. First-lactation cows (n = 263) had greater (P < 0.05) pregnancy rates (32 vs. 27%) than older cows (n = 391). The BCS at TAI ranged from 1.0 to 4.0. Cows having BCS #8805 2.25 (n = 469) had greater (P < 0.05) pregnancy rates than those having BCS < 2.25 (n = 185): 31% vs. 24%, respectively. For each 10-d increase in DIM at the first Presynch PGF injection, pregnancy rates increased (P < 0.05) by 9 ± 4%. We concluded that pregnancy rates for cows in which estrous cycles were presynchronized before the Cosynch-72 protocol were greater than those treated with the Cosynch-48 and Ovsynch protocols. Table 1. Pregnancy Rates at 40-41 Days after First Insemination Herd Cosynch-48 Ovsynch Cosynch-72 Total