Havemeyer Foundati<strong>on</strong> M<strong>on</strong>ograph Series No. 3RESULTS FROM EMBRYO FREEZING AND POSTOVULATION BREEDING IN A COMMERCIAL EMBRYOTRANSFER PROGRAMMEF. A. Lascombes and R. L. Pashen*Laboratorio Estancia ‘El Boyero’, C.C. 101 Casbas 6417, Provincia de Buenos Aires, Argentina;*Australian Animal Genetics Pty. Ltd., 54 Kalimna Drive, Morningt<strong>on</strong>, Victoria, 3931, AustraliaEMBRYO FREEZINGThe uteri <str<strong>on</strong>g>of</str<strong>on</strong>g> 20 d<strong>on</strong>or mares were flushedrepeatedly during a 70 day period with <str<strong>on</strong>g>the</str<strong>on</strong>g>intenti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> freezing any embryos collected. Aprevious unpublished study had indicated that largeembryos (≥ 220 µm) failed to develop when frozenand thawed but that those
Equine Embryo Transferdetected <strong>on</strong> ultrasound, and <str<strong>on</strong>g>the</str<strong>on</strong>g> operator thought<str<strong>on</strong>g>the</str<strong>on</strong>g>y would ovulate >24 h apart, mating wasdelayed until <str<strong>on</strong>g>the</str<strong>on</strong>g> first follicle had ovulated and thiswas followed by an iv injecti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> hCG (2,500 iu).Mares were re-mated prior to ovulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>sec<strong>on</strong>d follicle which usually occurred 24–36 hafter <str<strong>on</strong>g>the</str<strong>on</strong>g> first ovulati<strong>on</strong>.In mares with a single ovulati<strong>on</strong>, mating tookplace 2–14 h post ovulati<strong>on</strong>. The following resultswere obtained: <str<strong>on</strong>g>of</str<strong>on</strong>g> 13 recovery attempts performedfollowing matings 2–5 h post ovulati<strong>on</strong>, 11 (85%)yielded embryos. When mating occurred 6–8 hpost ovulati<strong>on</strong>, 15 <str<strong>on</strong>g>of</str<strong>on</strong>g> 16 flushes (94%) producedembryos. Following matings at 9–10 h postovulati<strong>on</strong>, embryos were recovered from2 <str<strong>on</strong>g>of</str<strong>on</strong>g> 3attempts (67%). Ten mares were mated >10 h postovulati<strong>on</strong> and <strong>on</strong>ly <strong>on</strong>e (10%) flush produced anembryo. These results show that acceptable rates<str<strong>on</strong>g>of</str<strong>on</strong>g> fertilisati<strong>on</strong> can be achieved when mares aremated up to 10 h post ovulati<strong>on</strong>.In mares with asynchr<strong>on</strong>ous twin ovulati<strong>on</strong>s,comparis<strong>on</strong>s were made between embryo collecti<strong>on</strong>rates when mating occurred before ovulati<strong>on</strong> andthose when mares were mated pre- and postovulati<strong>on</strong>. The following results were obtained:For pre-ovulati<strong>on</strong> mating in mares withovulati<strong>on</strong>s 24 h apart, 9 flushes (21%) produced noembryo, 15 (37%) produced <strong>on</strong>e and 18 (42%)produced 2. In mares with ovulati<strong>on</strong>s 36 h apart, 3flushes (17%) produced nothing, 8 (44%)produced <strong>on</strong>e embryo and 7 (39%) produced 2embryos. In mares with ovulati<strong>on</strong>s 48 h apart, 4flushes (31%) produced nothing, 5 (38%)produced <strong>on</strong>e embryo and 4 (31%) produced 2embryos. When mating occurred <strong>on</strong>ce before and<strong>on</strong>ce after ovulati<strong>on</strong>, and ovulati<strong>on</strong>s occurred 24 hapart, 3 flushes (15%) produced nothing, 7 (35%)produced <strong>on</strong>e embryo and 10 (50%) produced 2embryos. When ovulati<strong>on</strong>s were 36 h apart, 2flushes (22%) produced nothing, 5 (56%)produced <strong>on</strong>e embryo and 2 (22%) produced 2embryos. When ovulati<strong>on</strong>s were 48 h apart, 3flushes (27%) produced nothing, 2 (18%)produced <strong>on</strong>e embryo and 6 (55%) produced 2embryos. In all cases embryo recovery did notdiffer between <str<strong>on</strong>g>the</str<strong>on</strong>g> groups.In practice, when mares are mated postovulati<strong>on</strong>, flushing must be delayed for 24–36 h.O<str<strong>on</strong>g>the</str<strong>on</strong>g>rwise, embryo recovery is poor suggestingthat fertilisati<strong>on</strong> occurs up to 24 h after mating.96
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