Reducing the examination interval to detect ovulation below 12h does not improve pregnancy rates after postovulatory insemination with frozen/thawed semen in mares.

This research sought to determine whether increasing the frequency of examinations to detect ovulation in mares would improve pregnancy rates following insemination with frozen/thawed semen. Ultimately it found that examination intervals shorter than 12-15 hours did not significantly improve the rates of pregnancy or embryo loss.

Research Approach

• The research team used retrospective data collected over fourteen breeding seasons at an Equine Fertility Clinic, studying the impact of examination frequency on two main outcomes: pregnancy rate (PR) and embryo loss rate (ELR).
• Mares of various breeds and ages were observed in cycles varying from 0.5 to 15 hours before the ovulatory period up to the postovulatory period.
• When ovulation was detected in each cycle, a single dose of frozen-thawed semen was used for the insemination process.
• Post-insemination treatments including intrauterine antibiotics and oxytocin were applied to all mares.

Findings of the Study

• Pregnancy diagnoses were made between 12-17 days post-ovulation and continued in intervals up to 40 days, revealing an overall PR of 47.9%.
• The researchers divided the data into 3-hour examination intervals. For the first interval, mares were inseminated at the time of ovulation to 3 hours post-ovulation (n=44), with a PR of 43.2%.
• The following insemination in 3-hour intervals yielded PRs of 44.7% (3-6h, n=150), 45.1% (6-9h, n=432), 55.8% (9-12h, n=190), and 54.9% (12-15h, n=51).
• ELRs for the same 3-hour intervals were respectively 10.5%, 11.9%, 5.6%, 7.5% and 3.6%.
• The study found no significant statistical difference in either the PR or the ELR across intervals, leading to the conclusion that examining mares at intervals shorter than 12-15 hours did not improve PR or decrease ELR.

Conclusion

• The research indicated that in a post-ovulatory insemination regime using frozen-thawed semen followed by routine post-insemination treatment, there is no significant benefit to examining mares at intervals less than 12-15 hours for the intention of increasing pregnancy rates or reducing embryo loss rates.