THE EFFECT OF HORMONAL TREATMENTS ON THE PREGNANCY RATES OF MARES

Abstract

To determine the effect of hormonal drugs on the pregnancy rates of mares, authors analyzed this indicator in natural (n=303) and stimulated cycles (n=170). They used cloprostenol preparations to shorten the diestral period, and human chorionic gonadotropin [hCG] to induce ovulation. Natural cycles are divided into groups, depending on the duration – normal and short (19–24 and 12–18 days, respectively). Stimulated cycles for the following groups: (1) short (8–18 days); (2) normal (19–24 days) with the use of cloprostenol and hCG; (3) normal – with the use of hCG only. Short, both natural and stimulated cycles, are divided into groups – with normal (4–6 days) and short estrus (2–3 days). The analysis of natural and stimulated cycles showed that the level of pregnancy rates in stimulated cycles (73.5%–80.8%) corresponds to this indicator in normal natural cycles (79.6%). In natural short cycles, the pregnancy rate significantly decreases (26.3% ± 7.1%). When analyzing short cycles, it turned out that, both in natural and stimulated cycles, the pregnancy rate depends on the length of the estrus and decreases in cycles with a short estrus. In general, the difference in pregnancy rates was 41.0% (p ≤ 0.001). In short stimulated cycles, with an estrus length of 4–6 days, the pregnancy rate is higher (91.5% ± 4.06%) than in cycles with an estrus of 2–3 days (51.7% ± 9.3%). Thus, the shortening of the estrous period in stimulated cycles has a significant effect on the pregnancy rate.

Keywords

• cloprostenol
• human chorionic gonadotropin
• sexual cycle
• estrus
• diestrus
• ovulation
• pregnancy rates