The effect of HCG on duration of oestrus, ovulation time and fertility in mares.

This study investigates how the hormone HCG affects the menstrual cycle and fertility in horses. It found that administering HCG can alter the timing of ovulation and shorten the cycle, but does not significantly affect overall fertility rates.

Research Objective and Methodology

• The goal of this research was to understand the influence of Human Chorionic Gonadotropin (HCG), a hormone, on various aspects of a mare’s reproductive cycle. The researchers aimed to determine the impacts on the duration of oestrus (a period in the female reproductive cycle), the duration of dioestrus (the period between two oestrus periods), the length of the oestrous cycle, ovulation timing, and fertility.
• The research involved two separate experiments. In the first experiment, HCG injections were administered to non-lactating mares repeatedly across three consecutive cycles. Mares were given 2000 i.u. of HCG on the second day of oestrus during their initial cycle. In the second experiment, a single shot of 3300 i.u. of HCG was administered 24 hours before the first insemination during the initial cycle.

Results of Research

• In the first experiment, it was noted that the mares who received HCG had a shorter oestrus and ovulated more quickly than the control group (those that were not treated with HCG) during the first cycle. However, during the third cycle, the mares that were treated showed a longer oestrus and ovulated later compared to the untreated mares.
• The second experiment showed a reduction in oestrus duration by approximately 3.1 days with the administration of HCG. Even though the hormone influenced ovulation and the timing of the mare’s cycle, it did not significantly affect the pregnancy rate. The pregnancy outcomes were approximately similar between the treated (61.1%) and control group (63.9%).
• Despite this, fertility benefits were observed in the consecutive cycles after HCG treatment. The treated mares showed a higher conception rate. It was also seen that the number of insemination cycles required for achieving fertility was significantly less in treated mares across the three cycles.

Conclusion and Implications

• The research concluded that injections of HCG can influence the duration of oestrus and the time of ovulation in mares, with the effects showing considerable variance across different cycles.
• The study indicated that while HCG administration can change the reproductive cycle’s timing, it does not markedly impact the pregnancy rate. Nonetheless, it improves the conception rate in subsequent cycles and reduces the number of insemination cycles necessary to achieve fertility.
• These findings offer valuable insights for horse breeding and veterinary medicine, helping optimize the timing and plan reproductive procedures better for higher chances of successful conception.