The effect of the gonadotropin-releasing hormone analog, buserelin, on pregnancy rates in horse and pony mares.

Abstract We conducted a series of trials over a four-year period on a total of 2,346 mares, to determine the effect of a single dose of the GnRH analog buserelin (20 to 40 μg im or sc) on pregnancy rates when given between 8 and 12 days after service. Although there were some statistically significant improvements in pregnancy rates in individual trials, meta-analysis of the data overall showed significant improvements at all times examined, i.e. 13 to 16, 19 to 23, 28 to 31 and 38 to 42 days after service. These results indicate that treatment of mares with 20 to 40 μg buserelin between Days 8 and 12 significantly increases pregnancy rates by approximately 10 percentage points.