Embryo

Blastocyst Formation Rates In Vivo and In Vitro of In Vitro-Matured Equine Oocytes Fertilized by Intracytoplasmic Sperm Injection

Abstract
This study was conducted to evaluate in vivo and in vitro development of in vitro-matured equine oocytes fertilized by intracytoplasmic sperm injection. Oocytes were collected from slaughterhouse-derived ovaries, matured in vitro and injected with frozen-thawed stallion sperm. In vivo development was assessed after transfer of injected oocytes to the oviducts of recipient mares. Mares were euthanized 7.5 to 8.5 days after transfer and the uterus and oviducts flushed for embryo recovery. Of 132 injected oocytes transferred, 69 (52%) were recovered; of these, 25 (36%) were blastocysts with a blastocoele and capsule. In vitro development was assessed in three culture systems. Culture of zygotes in modified CZB medium with BSA, containing either 5.5 mM glucose for 7.5 d, or 0.55 mM glucose for 3d followed by 3 mM glucose for 2d, then 4.3 mM glucose for 2.5 d, did not result in blastocyst formation. Culture of zygotes in DMEM/F-12 with 10% FBS with and without co-culture with equine oviductal epithelial explants yielded 16 and 15% blastocyst development, respectively. Development to blastocyst was significantly lower in G1.3/2.3/BSA than in DMEM/F-12/BSA or in either medium with 10% added serum (2% vs. 18, 18 or 20%; P<0.05), suggesting that requirements for equine embryo development differ from those for other species. These results indicate that in vitro-matured equine oocytes are sufficiently competent to form 36% blastocysts in an optimal environment (in vivo). While we identified an in vitro culture system that provided repeatable blastocyst development without co-culture, this yielded only half the rate of development achieved in vivo.

Key words: Embryo • Assisted Reproductive Technology • Fertilization • In vitro fertilization • Ovum

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