A Single Post-Mating Uterine Infusion Of Penicillin Does Not Improve Pregnancy Rates In Maiden Thoroughbred Broodmares

Abstract

Past studies have found improved pregnancy rates in mares treated with post-mating intrauterine (IU) therapies and/or oxytocin. These treatments are thus commonplace in broodmare practice. In some instances, these treatments are given regardless of a mare’s history, current status and examination findings. The purpose of this study was to evaluate the effect of a single IU infusion of saline or procaine penicillin G on pregnancy and live-foal rate in maiden mares. Thirty-eight maiden Thoroughbred broodmares were evaluated over at total of 50 estrous cycles. All mares had a negative uterine culture prior to each mating. During each breeding cycle, all mares received 10 IU oxytocin (IM) 4-6 h after mating and either an infusion of physiologic saline (Control; n=24 cycles) or penicillin G (PPG; n=26 cycles) 16-24 h post-breeding. If a mare failed to become pregnant on her first cycle, another treatment was performed without consideration to the treatment given on the previous cycle. Day 0 was defined as the day of ovulation. Pregnancy status was determined by transrectal ultrasonography. Pregnancy rate per cycle was 72.00% (36/50), and Day 45 pregnancy and live-foal rates were 100% (36/36) and 90.6% (29/32), respectively. First-cycle pregnancy rates did not differ (P=0.278) between Control (83.3%; 15/18) and PPG cycles (65.0%; 13/20). No difference (P=1.0) was found in live-foal rates between Control (87.5%; 14/16) and PPG mares (93.8%; 15/16). These results indicate a single post-mating infusion does not appear to affect pregnancy and live-foal rates in maiden Thoroughbred mares.