Comparison of culture and insemination techniques for equine oocyte transfer

This study was designed to test 3 approaches for insemination and transfer of oocytes to recipient mares. Oocytes were recovered transvaginally from naturally cycling donor mares 24 to 26 h after an intravenous injection of 2500 IU of hCG when follicles reached 35 mm in diameter. Multiple oocytes (1 to 4) were transferred surgically into the oviducts of 4 or 5 recipient mares per group. Three groups of transfers were compared: 1) transfer of oocytes cultured in vitro for 12 to 14 h postcollection with insemination of the recipient 2 h postsurgery; 2) transfer of oocytes into the oviduct within 1 h of collection, with completion of oocyte maturation occurring within the oviduct, and insemination of the recipient 14 to 16 h postsurgery; and 3) transfer of spermatozoa and oocytes (cultured 12 to 14 h in vitro) into the oviduct. Numbers of embryos detected by Day 16 of gestation were not different (P>0. 1) for groups 1, 2, and 3 (57%, 43% and 27%). Therefore, equine oocytes successfully completed the final stages of maturation within the oviduct, and sperm deposited within the oviduct were capable of fertilizing oocytes.