Influence of co-culture during maturation on the developmental potential of equine oocytes fertilized by intracytoplasmic sperm injection (ICSI).

The influence of co-culture with either oviduct epithelial cells or fetal fibroblast cells on in vitro maturation of equine oocytes and their potential for development to blastocysts and fetuses after intracytoplasmic sperm injection (ICSI) was investigated. The oocytes were obtained from ovaries from abattoirs and were matured in vitro for 28-30 h in TCM-199 only, or in TCM-199 co-culture with oviduct epithelial cells or fetal fibroblast cells. Metaphase II oocytes were subjected to ICSI with an ionomycin-treated spermatozoon. The injected oocytes were cultured for 7-9 days in Dulbecco's modified Eagle's medium. Morphologically normal early blastocysts were transferred to the uteri of recipient mares. Nuclear maturation rates and the rates of cleavage to the two-cell stage for injected oocytes were similar in the groups of oocytes that were matured in TCM-199 (49 and 63%), in co-culture with oviduct epithelial cells (53 and 65%) or in co-culture with fetal fibroblasts (51 and 57%). There were no significant differences in the proportions of blastocysts that developed from the two-cell embryos derived from oocytes matured by co-culture with either oviduct epithelial cells (30%) or fetal fibroblasts (17%). However, significantly higher proportions of blastocysts were produced from both these co-culture groups than from the groups of oocytes matured in TCM-199 only (P < 0.05). Six of the blastocysts that had developed from oocytes co-cultured with oviduct epithelial cells were transferred into recipient mares and four pregnancies resulted. These results demonstrate a beneficial influence of co-culture with either oviduct epithelial cells or fetal fibroblasts for maturation of oocytes in vitro.