PSX-6 Effects of administration of a non-specific immunostimulant prior to timed artificial insemination on pregnancy per artificial insemination in mature beef cows.

Abstract The objective of the present study was to determine whether administration of a non-specific immunostimulant prior to timed artificial insemination (TAI) could improve pregnancy per artificial insemination (P/AI). Mature beef cows [59.2 ± 0.77 days postpartum (mean ± SEM)] consisting of a stabilized composite (1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise) were submitted to synchronization and TAI during two successive breeding seasons (Year 1: n = 297; Year 2: n = 248). For synchronization, cows received the 7-d CO-Synch + CIDR protocol [100 μg of gonadotropin-releasing hormone (GnRH), i.m., and a controlled internal drug releasing device (CIDR) was inserted intravaginally on d -9; CIDR removal plus prostaglandin F2α (25 mg, i.m.) on d -2 with TAI on d 0]. On d 0, approximately 50 ± 2 h following CIDR removal, cows were randomly treated with 5 ml, i.m., of either sterile saline or mycobacterium cell wall fraction (MCWF; Amplimune, Novavive) and cows that had not exhibited estrus were administered a second dose of GnRH (100 μg, i.m.). All cows were submitted to TAI at approximately 56 ± 4 h following CIDR removal using frozen-thawed semen from 1 of 16 randomly selected bulls (n = 8 different bulls within breeding season). Pregnancy was initially diagnosed at d 35-60 (PREG1) and subsequently confirmed at d 105-110 (PREG2) of gestation. Data was analyzed using the Proc Glimmix procedure of SAS with year, treatment, estrus, sire(year), AI technician and all two-way interactions considered as independent variables. Overall, there was no effect of MCWF treatment prior to TAI on PREG1 (Saline: 130/267 = 48.7% vs. MCWF: 132/274 = 48.2%; P = 0.87) or PREG2 (Saline: 129/269 = 47.8% vs. MCWF: 130/274 = 47.2%; P = 0.80) and there was no interaction between year and MCWF treatment for PREG1 (P = 0.32) or PREG2 (P = 0.26). While there was no overall effect of sire, PREG1 and PREG2 were affected by a sire x treatment interaction (P = 0.04). Additionally, P/AI was affected by estrus response. Specifically, cows that exhibited estrus prior to TAI had greater P/AI at both PREG1 (135/236 = 57.2% vs. 127/308 = 41.2%; P = 0.0001) and PREG2 (136/235 = 57.9% vs. 123/308 = 39.9 %; P = 0.0001) than for cows that did not exhibit estrus. There was no interaction between treatment and exhibition of estrus prior to TAI for either PREG1 (P = 0.83) or PREG2 (P = 0.87). Pregnancy loss between PREG1 and PREG2 was not affected by any of the independent variables analyzed. Results indicate that treatment with a non-specific immunostimulant prior to TAI does not impact P/AI or pregnancy loss in mature beef cows.