Steven H. Slusher, Equine Theriogenologist; Carolynn Taylor-MacAllister, Extension Veterinarian; David W. Freeman, Extension Equine Specialist, Oklahoma State University
The vast majority of stallions are hand-mated naturally or collected for artificial insemination. While total conception rates are no less with pasture breeding, most mare owners require specific breeding dates so that expected foaling dates can be accurately calculated.
Conception rates are highest when mares with reasonably good fertility are mated to stallions which meet high fertility standards (semen volume, sperm concentration, and percentage of live sperm).
Mares with unknown or poor reproductive histories should be evaluated by using the standard practices of palpation, ultrasonography, intrauterine culture, cytology, and biopsy well ahead of the breeding season (i.e., late summer or early fall of the previous season) or as problems appear during the current breeding season. A “clean culture” by itself may not reveal the reproductive problems of an individual mare.
Early detection of reproductive abnormalities, followed by proper therapy and management changes, usually results in more consistent and acceptable conception and foaling rates.
Conception rates are highest when mares are inseminated 36 hours before and up to the time of ovulation. As previously stated, ovulation most frequently occurs 24 to 48 hours prior to the end of estrus.
Ovulation can be easily missed unless managers are precise in estrus detection and maintain accurate records. Managers often start breeding mares the second or third day of estrus (heat) and continue every other day until the mares goes out of estrus.
However, palpation and ultrasonography can aid significantly in calculating the proper breeding time.