Developmental capacity of equine oocytes matured and cultured in equine trophoblast-conditioned media

Abstract

The objective was to compare culture media for in vitro maturation of equine oocytes and for in vitro culture of zygotes produced from IVF of partially zona-removed oocytes. Cumulus-oocyte complexes from slaughterhouse-derived ovaries were washed in m-Dulbecco's PBS and cultured in TCM-199, F10-DMEM or c-F10-DMEM (50% F10-DMEM + 50% F10-DMEM conditioned medium from culture of an equine trophoblast monolayer for 3 or 4 days). All media included FSH, LH, E 2, and 10% FCS. After 28 to 30 h maturation, cumulus expansion was scored from 0 (no expansion) to 4 (fully expanded). Oocytes with a 1st polar body were selected for manipulation after removing cumulus cells using hyaluronidase. About one-third of the zona pellucida was cut using a fragment of a razor blade. For fertilization, fresh stallion semen was washed twice in BGM3 (a modified Tyrode's medium) and capacitated with 0.5 mM c-AMP for 3.5 h and 100 μM ionomycin for 15 min and added to oocytes in fert-TALP at 10 6 spermatozoa/mL. After 20 h, some presumptive zygotes were stained, and the rest were cultured in 100% TCM-DMEM conditioned medium. Cumulus expansion in F10-DMEM and c-F10-DMEM was higher (P<0.05) than the TCM-199 control (3.2, 3.5 vs 1.3, on a scale of 0 to 4). However, polar body formation rates were not different among treatments (47, 52 and 50%). The fertilization rates of equine oocytes matured in TCM-199, F10-DMEM and c-F10-DMEM determined by fixing and staining were 41, 35 and 29%, with no significant differences. There were no significant differences among treatments in cleavage rates (36 to 40%), development to morula (3 to 10%), or blastocyst stages (3 to 5%). On Day 14 of culture in c-F10-DMEM treatment, one blastocyst had more than 500 nuclei, but no capsule was formed. In a further study, cleavage rates (46 to 50%) and development to morula (5 to 10%) and blastocyst stages (3 to 8%) were not different (P>0.1) between TCM-DMEM and 100% conditioned TCM-DMEM for culturing embryos. Six embryos (2 morulae and 4 blastocysts) were nonsurgically transferred to 4 recipient mares, but no pregnancy continued.