Use of parentage testing to determine optimum insemination time and culture media for oocyte transfer in mares.

This research studied the best time to inseminate mares and the most effective culture medium for growing horse oocytes, or egg cells, for transfer. The results determined that the optimal timing for insemination was 15 hours before oocyte transfer, and the Tissue Culture Medium (TCM-199) was superior for oocyte culture compared to the Equine Maturation Medium I (EMMI).

Research Methodology

• Oocytes were collected from mares approximately 22 hours after the administration of human chorionic gonadotropin, a hormone that stimulates ovulation.
• The oocytes were then cultured for roughly 16 hours in one of three media (special solutions for growing cells), with or without additional hormones and growth factors.
• Groups of three or four oocytes, each cultured in different media, were transferred to the recipient mare’s oviduct (part of the female reproductive system) on the opposite side from the recipient’s own ovulation.
• Finally, recipients were inseminated with semen from two different stallions: once 15 hours before and once 2.5 hours after the oocyte transfer took place.

Key Findings

• Embryos were recovered from the uteri about 16 days after transfer and were tested for parentage to assess the success of the transfers.
• The study found no significant difference between the number of embryos resulting from transferred oocytes and those resulting from the recipients’ own ovulated oocytes.
• Importantly, the researchers determined that far more oocytes were fertilized from insemination prior to oocyte transfer, compared to after transfer.

Best Culture Medium and Time of Insemination for Oocyte Transfer

• The study concluded that Tissue Culture Medium (TCM)-199 was a better solution for culturing oocytes than Equine Maturation Medium I (EMMI), a Serum Osmolarity Fluid (SOF)-based medium.
• The addition of hormones and growth factors during culture did not improve the development of embryos, suggesting these additions are not necessary for successful oocyte culture and transfer.
• In terms of timing, insemination 15 hours before the oocyte transfer resulted in very high fertilization rates, indicating this to be the best time frame for insemination in procedures involving oocyte transfer.