Production, Management and the Environment: Reproduction and Health Management

The objective was to evaluate whether addition of EAZI-BREED CIDR Cattle Inserts (CIDR) to the Ovsynch program increases first service pregnancy rate (PR) in lactating dairy cows. The study was conducted in 5 dairies in Central Mexico. Cows were inseminated from June through September, 2001. Within trial site and within parity, cows were assigned to either an Ovsynch (n=255) or an Ovsynch-CIDR group (n=255) for their first service. Ovsynch was initiated at 50±3 d postpartum with an injection of 100 μg of GnRH (2 mL, i.m.; CYSTORELIN), an injection of 25 mg of PGF2α (5 mL, i.m.; LUTALYSE Sterile Solution) 7 d later, a second 100 μg injection of GnRH 48 h later, and timed insemination 8 to 20 hours after the second GnRH injection. Ovsynch-CIDR cows received the same treatments but also received a CIDR Insert (1.38 g of progesterone) which was administered with the first GnRH injection and removed 7 d later at the PGF2α injection. Cows were palpated for pregnancy 40 to 45 d after timed insemination. An interaction between treatments and parity was detected (P=0.023). The interaction indicated that PR was increased for Ovsynch-CIDR compared to Ovsynch in primiparous cows (38.2% and 20%, respectively; P=0.024) but no differences were detected in multiparous cows (22.3% and 27.5%, respectively; P=0.375). A subset of cows (n=466) was classified as anestrus or cyclic based on progesterone concentrations of two blood samples collected 7 d prior to and at the first GnRH injection. For anestrous cows, PR was 18.8% for Ovsynch (6/32) and 18.4% for Ovsynch-CIDR (7/38). For cyclic cows, PR was 23.5% for Ovsynch (47/200) and 29.1% for Ovsynch-CIDR (57/196). Such effects were further subdivided according to parity but none were significant. Addition of CIDR increased first service pregnancy rates of primiparous but not multiparous lactating dairy cows submitted to an Ovsynch program. Because cows were inseminated during summer, heat stress might have affected embryonic survival but the study was not designed to specifically address such an effect.