The article presents the results of analysis pregnancy rates mares depending on duration intervals from cloprostenol preparation injection to ovulation. It was found that with a decrease in interval (≤7 days), rate decreases by 30% (p≤0.05). To determine optimal time for use, an ovulation performed, day sexual cycle and largest follicle diameter. average before groups, (5, 6-7, 8-10, 11-15 have...