Successful equine in vitro embryo production by ICSI – effect of season, mares’ age, breed, and phase of the estrous cycle on embryo production.

The study investigates the impact of different factors on the effectiveness of in vitro horse embryo production through intracytoplasmic sperm injection (ICSI). Findings suggest that factors such as breed, age, stage of estrous cycle at the time of the procedure, and season all have significant influence on the success rate of the method.

Research Design and Methodology

• This research is based on a retrospective analysis which aimed to determine the various factors influencing the success of horse embryos’ in vitro production by ICSI.
• A total of 7993 ovum pick-up (OPU) procedures were conducted spread across 2540 donor mares with semen from 396 different stallions.
• The oocytes were collected from multiple locations in Brazil and transported to the laboratory within six hours from the procedure in a pre-maturation medium.
• Subsequently, the in vitro maturation (IVM) process was carried out, followed by ICSI and in vitro culture of the embryo for a period of 7-8 days.

Key Findings

• The study established that the age and breed of the donor mare, the season of the year in which the procedure was carried out, and the stage of estrous cycle on the day of follicular aspiration all significantly impacted the number of recovered oocytes, matured oocytes, cleaved embryos, and blastocysts.
• Mares aged between 6 and 15 years had a generally higher success rate in almost all the evaluated parameters as compared to other age groups particularly the average number of blastocysts per OPU session. This age-related impact was observed to be consistent across two breeds – American Quarter Horse (AQHA) and Warmblood mares.
• The breed of the mare made a substantial difference to key parameters including the number of oocytes recovered, blastocysts produced per OPU session, and blastocyst rates. The surveyed breeds included AQHA, Warmblood, Crioulo, Lusitano, and Mangalarga.
• Although season had less of an impact than the breed and age, the rate of oocyte maturation was found to be higher during the summer season.
• The stage of estrous at the time of OPU also influenced the success of the process. Follicular phase mares, with or without dominant follicle, generally performed better than luteal phase mares.

Conclusion

• The study concluded that breed, age, season, and the stage of estrous at the time of OPU all significantly impact the success of equine embryo production by ICSI.
• The ICSI technology allows for year-round production of embryos from mares of varying breeds and ages using oocytes collected from multiple sites.