Effect of Timing of Post-ovulatory Insemination Relative to hCG/BuserelinTreatment with 1 Straw of frozen-thawed semen on Mare Fertility

Abstract The reproductive management of mares for frozen semen artificial insemination (AI) can be costly and labor intensive. Predicting the exact time of ovulation can be challenging, even when ovulation inducing drugs are used. The main objective of this retrospective study was to determine whether there was an effect of interval between examinations to detect ovulation on likelihood of pregnancy and early embryonic loss (EEL) in mares following post-ovulatory breeding with a single straw of frozen/thawed semen. Second objective was to determine the efficacy of two different drugs (hCG vs. buserelin) for timely induction of ovulation. Length of the interval from penultimate check to ovulation had no significant effect on pregnancy or embryo loss rates (4 h: 34.1% and 13.3% vs. 8 h: 26.1% and 0% and 16 h: 34.5% and 10%, respectively); nor did the ovulation inducing drug used,number of the cycle or the stallion. In conclusion, there appears to be no advantage of checking mares for ovulation during the late evening and night hours when using a post-ovulatory AI protocol and ovulation-inducing drugs.