Effect of type of semen, time of insemination relative to ovulation and embryo transfer on early equine embryonic vesicle growth as determined by ultrasound.

The research explores how different horse breeding protocols impact the growth of the embryonic vesicle, an early stage of equine pregnancy. It specifically looked at the timing of insemination in relation to ovulation, the type of semen used, and whether an embryo transfer takes place.

Research Context and Methodology

• This study builds on previous research exploring how certain commonly used breeding approaches can influence early equine pregnancy, specifically the growth of the embryonic vesicle (the fluid-filled structure that develops around the embryo).
• The research examines 159 pregnancies that were a result of four different mating protocols: pre-ovulation natural mating, pre-ovulation natural mating followed by transfer into surrogate mares, post-ovulation natural mating, and post-ovulation artificial insemination using thawed, frozen sperm.
• The presence and size of the embryonic vesicles in the resulting pregnancies were tracked via ultrasound from day 12 to day 19 of pregnancy, and the data was statistically analyzed to determine any effects of the different mating protocols on growth.

Main Findings

• Analysis of the data revealed no significant difference in embryonic vesicle size between pre-ovulation natural mating and pre-ovulation natural mating followed by embryo transfer. Similarly, no significant difference was found between post-ovulation natural mating and post-ovulation artificial insemination.
• However, it was discovered that the timing of insemination relative to ovulation had a significant impact on embryonic vesicle size. Specifically, vesicles were generally larger in pregnancies resulting from pre-ovulation inseminations (either natural or followed by transfer) compared to those resulting from post-ovulation inseminations (either natural or artificial).
• The decrease in vesicle size associated with post-ovulation insemination corresponded to roughly one day’s worth of growth, suggesting that the timing of insemination may delay early embryonic development.

Research Conclusion

• The research concluded that the timing of insemination in relation to ovulation plays a crucial role in the early development of equine pregnancy, represented by the size of the embryonic vesicle.
• Moreover, the study found no significant impact of the type of semen used (fresh or frozen-thawed) on early embryonic growth, nor of whether an embryo transfer took place after fertilization.
• Therefore, the researchers emphasized the importance of pre-ovulation insemination to achieve optimal embryonic vesicle growth, which should be further evaluated for potential impacts on pregnancy success rates and long-term health of the foals.