Comparison of pregnancy rates from transfer of fresh versus cooled, transported equine embryos.

This study investigates and compares the success rates of pregnancy in mares from the transfer of fresh horse embryos and embryos that were cooled and transported. The results indicate that both the fresh and cooled embryos have similar rates of inducing successful pregnancies, showing that equine embryos can be cooled and stored for up to 24 hours without any reduction in fertility.

Research Methodology

• The study was conducted with donor mares of various light-horse breeds, and sources of embryos were split into two groups: 104 fresh embryos obtained directly and 136 cooled embryos shipped from various U.S breeding farms to Colorado State University.
• Embryos were harvested seven days after the mares’ ovulation, assessed for quality, and either transferred into a recipient mare immediately or stored in a specific solution and cooling unit before being shipped to a laboratory.
• Upon arrival, the cooled embryos were also graded in terms of quality and size, and then surgically transferred into synchronized recipient mares.
• These recipient mares had ovulated either one or two days before, on the same day, or one to three days after the ovulation of the donor mare.

Assessing Pregnancy

• The success of the embryo transfer was determined by ultrasonography on day 12, 35, and 50 post the donor mare’s ovulation.
• The pregnancy rates at these intervals were recorded for both fresh and cooled embryos, with similar percentages found for both treatments.

Findings of the Study

• The size and quality grading of the embryos were found to significantly affect the pregnancy success rates at all checked intervals. High-quality embryos were more likely to result in successful pregnancies than those of lower grades.
• The researchers found no significant difference between the rates of embryonic loss (failure for the embryo to develop) between day 12 and 35, or between 35 and 50, regardless of whether they were fresh or cooled embryos.
• However, embryonic losses were found to be higher for those embryos stored for more than 12 hours compared to those stored for less than 12 hours before transfer.
• The duration required for shipping cooled embryos, whether they were stored for less than or more than 12 hours, did not affect the pregnancy rates recorded at day 12 post the donor’s ovulation.
• The age of the donor mare was found not to have an effect on the success rates of the pregnancy or the quality of the embryos, regardless of whether they were fresh or cooled.

Conclusions

• Overall, the study concludes that equine embryos can be cooled down to 5 degrees Celsius and can be stored safely for up to 24 hours without a decrease in fertility compared to fresh embryos that were transferred within an hour of harvesting.