Effects of time of insemination relative to ovulation on pregnancy rate and embryonic-loss rate in mares.

The research article investigates the impact of timing of insemination in relation to ovulation on the rates of pregnancy and embryonic loss in mares. The research demonstrates that precise timing of insemination significantly affects these rates.

Objective & Methodology

• The primary objective was to analyze how timing of insemination, specifically pre-ovulatory and post-ovulatory, affects pregnancy and embryonic loss rate. For this purpose, 268 mares were studied over two experiments.
• The mares within each experiment were sorted randomly into three groups based on the insemination timing: when the pre-ovulatory follicle was 35mm (pre-ovulatory group); on the day of ovulation (Day 0 group); and the day after ovulation (Day 1 group).
• Ultrasonic pregnancy tests were performed on various days post-insemination to track the progression of each potential pregnancy.

Findings

• The results showed significant differences in pregnancy rates between the three groups. More specifically, in Experiment 2, the pregnancy rate was lower in the pre-ovulatory group when insemination occurred 4 days or more before ovulation versus up to 3 days before ovulation.
• The Day 0 group showed a lower pregnancy rate when compared to the pre-ovulatory group where insemination took place up to 3 days prior to ovulation.
• Interestingly, for mares in Experiment 2 where ovulation was carefully monitored, those inseminated 0 to 6 hours after ovulation had a higher pregnancy rate than those inseminated 18 to 24 hours after ovulation. Insemination 30 hours or more after ovulation yielded no successful pregnancies.
• Additionally, there were significant differences observed in the day of first detection of the embryonic vesicle among the three groups and differences in the diameter of the embryonic vesicle averaged over Days 11 to 15 between the groups.

Conclusion

• Overall, the timing of insemination relative to ovulation significantly impacts pregnancy and embryonic-loss rates in mares.
• These results can provide valuable insights for establishing effective breeding strategies for mares and potentially other mammal species too.