Embryonic development after intra-follicular transfer of horse oocytes.

A technique was developed in which immature horse oocytes, obtained from slaughterhouse specimens, were transferred to the pre-ovulatory follicle of a mare in vivo, with resulting oocyte maturation, ovulation, fertilization and embryo development. Oocytes were collected from all follicles greater than 3 mm, and were classified as immature, maturing, expanded or denuded. The transfers were performed in the standing, tranquilized mare. The ovary containing the pre-ovulatory follicle was grasped per rectum. A trochar and cannula were placed through the abdominal wall in the flank area, ipsilateral to the grasped ovary. For the transfer, the operator introduced a needle through the cannula to puncture the outer wall of the follicle, while adjusting the position of the ovary per rectum. The mares were inseminated the day after transfer. Twenty oocyte transfers were performed. In 1 mare, 15 immature oocytes were transferred to the pre-ovulatory follicle and 12 oocytes with expanded cumuli were recovered from the follicle 24 h later. In 3 of the remaining 19 mares, the follicle filled with blood after the transfer and ovulation did not occur. Sixteen mares ovulated after oocyte transfer. One mare was killed 3 days following ovulation; flush of the removed oviduct yielded 1 embryo, 2 recently ovulated oocytes and 3 degenerating oocytes. A uterine flush for embryo recovery was performed in each of the other 15 ovulating mares, 7-11 days after ovulation. Embryos were recovered in 7 of the 15 flushes, and embryos in excess of the number of ovulations were recovered from 4 mares (2, 3, 4 and 7 embryos).