The effect of time of mating (with respect to time of ovulation) on fertility and early embryonic death (EED) in the equine was quantified. Thoroughbred mares (n= 405) were observed during 629 estrous cycles. The mares were divided into five groups: I- 79 mares that were mated between 48 and 36 hours prior to ovulation; II- 102 mares that were mated between 36 and 24 hours prior to ovulation; III- 166 mares that were mated between 24 and 12 hours prior to ovulation; IV- 185 mares that were mated between 12 hours prior to ovulation and the time of ovulation; and V- 97 mares that were mated during the interval from ovulation to 12 hours after ovulation. The occurrence of an ovulation was determined by rectal palpation and ultrasonography, performed every 12 hours. The diagnosis of conception was done 14 days after mating with the help of ultrasonography. Ultrasonography examination to detect EED was done on the 60th day post-mating. Conception rates were highest in groups III and IV (P<0.06). The regression analysis verified a quadratic model for successful pregnancy 14 days (R² = 91.0%; P<0.05) and 60 days (R² = 89.2%; P<0.05) post-mating. Although groups did not differ significantly in EED, regression analysis verified a quadratic model (R² = 92.4%; P<0.05). Results suggest that the optimum time for mating is the interval from 24 hours prior to ovulation up to the time of ovulation.
equine; mating time; ovulation; fertility; embryonic death
