In vitro maturation and fertilization of domestic cat follicular oocytes

The time course and conditions necessary for oocyte maturation and subsequent fertilization in vitro were studied in the domestic cat. Darkly pigmented oocytes surrounded by cumulus cells and a tight corona radiata were collected from ovaries removed at ovariohysterectomy. After culture in Eagle's minimum essential medium, oocytes were evaluated for nuclear maturation by analyzing chromosomal spreads. Oocytes achieved metaphase II after intervals of 40-48 hr of in vitro incubation. The incidence of maturation was enhanced (P less than 0.05) when oocytes were recovered from inactive (54%) or follicular (56%) stage donors compared to those recovered from luteal phase (29%) or pregnant (35%) cats. The proportion of oocytes successfully maturing in vitro in medium containing no hormone supplementation (37%) was less (P less than 0.01) than counterparts cultured in follicle-stimulating hormone (FSH) only (48%) or FSH and luteinizing hormone (LH) (54%). The efficiency of maturation was not influenced (P greater than 0.05) by either maintenance/transport temperature (4 degrees C vs. 22 degrees C) or delaying recovery of oocytes from antral follicles (2-8 hr vs. 24-32 hr). Approximately 36% of the in vitro matured oocytes cocultured with spermatozoa demonstrated evidence of fertilization; however, there appeared to be a critical development period for maximizing the incidence of fertilization. These results demonstrate that domestic cat antral oocytes are capable of maturing in vitro, and maturation is influenced by the reproductive status of the donor and the presence of gonadotropins in the culture medium. These oocytes are capable of forming embryos and developing to at least the 16-cell stage in vitro.