Pregnancy rates following administration of GnRH to anestrous mares

Summary The objective of the study was to compare pregnancy rates in seasonally anestrous mares induced to ovulate by administration of GnRH plus a single injection of hCG once a follicle > 35 mm was detected versus pregnancy rates at ovulations hastened by hCG in transitional mares. Seventy two percent of seasonally anestrous mares treated with GnRH plus hCG in mid-February ovulated. The pregnancy rate for mares receiving GnRI-I plus hCG (77.8%) was not signifi- cantly different (p>0.05) than the pregnancy rate for mares receiving hCG after spontaneous follicular development during the transition period (85.2%). The rate of early em- bryonic loss in the GnRH treated mares (7.1%) was similar to rates previously reported for reproductively normal brood- mares (9.0 - 11.1%). This supports the concept that GnRH administration followed by hCG is a suitable method of inducing fertile ovulations in seasonally anestrous mares.