Fertility of mares after postovulatory insemination.

The research article discusses a study on the fertility of mares after insemination post-ovulation. The study found that all mares inseminated within 18 hours of ovulation conceived. However, the conception rate dropped significantly, and no mare conceived if inseminated 24 hours or more after ovulation. Additionally, a high incidence of early embryonic death was observed, suggesting a decrease in embryo viability.

Methodology

• The research consisted of two experiments. In the first experiment, 11 Finnhorse mares were observed during their late oestrus cycle using rectal palpation and ultrasonography to determine the exact time of their ovulation.
• The mares were then inseminated for one to three subsequent cycles at varying hours post-ovulation: 6-12, 12-18, 18-24, and 24-30 hours. Any pregnancy resulting from the insemination was terminated after 21 days using a prostaglandin injection for research reliability.
• In the second experiment, 14 mares were observed and inseminated post-ovulation within a range of 0-27 hours. Similar to the first experiment, any pregnancy was terminated after 25 days with a prostaglandin injection.

Findings

• In the first experiment, a total fertility rate of 100% was observed for all mares inseminated within 18 hours post-ovulation. However, none of the mares inseminated beyond 24 hours post-ovulation conceived, indicating a narrow fertility window.
• In the second experiment, around 46% of mares (13 out of 28) became pregnant 16 days post-insemination. However, five pregnancies ended with early embryonic death, meaning ultimately only around 29% of the mares remained pregnant.
• The investigation suggests that the ovum of the mare remains receptive to fertilization for at least 18 hours post-ovulation. However, it also indicates a potential decrease in embryo viability, evidenced by the high rate of early embryonic death recorded in the second experiment.