Folliculogenesis, embryo parameters and post-transfer recipient pregnancy rate following equine follicle-stimulating hormone (eFSH) treatment in cycling donor mares.

The research studied the effects of equine follicle-stimulating hormone (eFSH) treatment on the success rate of embryo transfer programs in horses. The study found that though eFSH treatment stimulated the horse’s ovary and produced more embryos, the quality of these embryos was lower and the pregnancy rate in recipient mares was less than expected.

Study Design

• The researchers conducted the study at the University of Saskatchewan in Canada using a total of 49 mares, 12 of which were donors and 37 recipients. The study was completed during the physiological breeding season.
• The donor mares underwent two consecutive oestrous cycles. In the first one, which acted as a control cycle, the mares were given human chorionic gonadotropin (hCG) to induce ovulation. In the second cycle, referred to as the eFSH cycle, the mares received eFSH treatment.
• eFSH treatment was administered twice daily as soon as a 25mm follicle was detected. The treatment ceased when a follicle of 35mm emerged. At this point, hCG was administered like in the control cycle.
• All donor mares were artificially inseminated while in oestrus using fresh semen collected from a stallion of proven fertility. On the 8th day following ovulation, embryos were extracted transcervically and individually transferred to a synchronised recipient mare.

Results

• The eFSH treatment successfully stimulated the mares’ ovaries, resulting in a higher number of ovulations and recovered embryos compared to the control cycle.
• However, the embryos resulting from eFSH treatment tended to score lower on morphological grade, indicating they were of lesser quality compared to the control embryos.
• The pregnancy rate in recipient mares for each transferred embryo was lower than anticipated in the eFSH cycle.

Conclusions

• The overall number of pregnancies and foals born from the eFSH-treated embryos was not significantly different from the control cycle.
• Despite the increased number of embryos produced under eFSH treatment, the lower quality and reduced pregnancy success rate indicate that eFSH treatment may not significantly enhance the efficiency of embryo transfer programs in mares.