Factors affecting pregnancy rates in mares bred with cryopreserved semen.
Authors: Pasch L, Stefanovski D, Dobbie T, Lewis G, Turner R M
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Reproductive practitioners have traditionally relied on substantial cryopreserved semen doses—eight 0.5 ml straws containing roughly 800 million total sperm—yet commercial trends are shifting towards single-straw breeding doses delivered via deep horn artificial insemination, prompting Pasch and colleagues to investigate whether dose reduction compromises conception rates. Their analysis of pregnancy outcomes across multiple mares revealed no significant difference in success whether mares received one straw or the full traditional complement, nor did timing of insemination relative to ovulation (0–3 hours versus 0–6 hours post-ovulation) or single versus double insemination protocols affect pregnancy outcome. Surprisingly, classical markers including post-thaw progressive motility, endometrial bacterial culture results, and post-breeding uterine fluid accumulation showed no association with conception success. The findings suggest a robust market-driven quality filter is operating within the breeding industry, whereby only semen from the most fertile stallions enters ultra-low-dose commercial channels, effectively pre-selecting for resilient spermatozoa tolerant of cryopreservation and single-straw deployment. For practitioners, this work supports confidence in contemporary minimalist insemination protocols and indicates that obsessive adherence to narrow ovulation windows or bacterial monitoring may offer less clinical value than previously believed when working with commercially available cryopreserved doses.
Read the full abstract on PubMed
Practical Takeaways
- •Ultra-low dose breeding protocols (single 0.5 ml straws) appear viable for cryopreserved semen, likely due to industry self-selection of highly fertile stallions—reducing semen costs without compromising pregnancy rates
- •Single post-ovulation insemination simplifies breeding management and reduces farm visits without sacrificing fertility outcomes compared to dual insemination strategies
- •Strict timing of insemination within 3 hours post-ovulation is unnecessary; breeding within 6 hours post-ovulation achieves equivalent pregnancy rates
Key Findings
- •Number of 0.5 ml straws (ranging from 1 to 8) had no effect on pregnancy outcome in mares inseminated with cryopreserved semen
- •Single post-ovulation insemination was equivalent to pre- and post-ovulation insemination for pregnancy rates
- •Breeding within 0-3 hours post-ovulation provided no advantage over breeding within 0-6 hours post-ovulation
- •Endometrial bacterial culture results, post-thaw sperm motility, and post-breeding uterine fluid accumulation did not significantly impact pregnancy outcome