Effect of estrous cycle stage on oocyte in vitro maturation of domestic cats reared under tropical conditions

Oocyte maturation is a critical step for in vitro embryo production. In female cats, findings on the influence of the estrous cycle stage on oocyte quality and maturation are contradictory. Little is known about this phenomenon in female cats in the tropics. This study aimed to assess the effect of the estrous cycle stage on oocyte quality and subsequent capacity to complete nuclear maturation in cats in a tropical environment. Ovaries from 18 sexually matured cats were collected during ovariohysterectomy. Cumulus–oocyte complexes (COCs) were released from follicles by slicing and fragmentation of the ovarian cortex. According to morphological characteristics, COCs were classified into grades I–II (suitable) and III–IV (no suitable). Only suitable COCs from each cat were cultured for in vitro maturation. Nuclear oocyte maturation was assessed by the presence of a telophase I or metaphase II plate with extrusion of the first polar corpuscle. A significantly greater number of oocytes per ovary were collected from queens in inactive than in follicular or luteal phase. Proportions of suitable COCs were similar among groups. Rate of oocyte maturation did not differ among stages of the estrous cycle, nor did the proportion of non–matured or degenerated oocytes. The age of the queens did not affect the percentage of oocyte maturation. In conclusion, the quality and rate of oocytes maturation were similar in the three stages of estrous cycle examined.