Oocyte quality of small antral follicles coexisting with cystic follicles in the ovaries of the cow.

The present study was conducted with ovaries to evaluate the effect of the presence of a cystic follicle and its steroid hormone concentration on the oocyte recovery rates, oocyte morphology and in vitro maturation of the oocytes from coexisting small follicles. Ovaries, each bearing a follicular cyst (containing > 10 ml of follicular fluids, > 3 cm in diameter, and without a functional corpus luteum), were collected from each of the 26 Holstein cows from a local slaughterhouse. Small follicles (1-7 mm) from these ovaries were aspirated and their cumulus-oocyte complexes (COCs) classified into one of 5 groups (A to E), depending on oocyte and cumulus cell morphologies. Those oocytes with compact cumulus cells were cultured and their maturation rates determined. Concentrations of estradiol-17 beta (E2) and progesterone (P4) were measured in cystic follicular fluid using double antibody enzyme immunoassays (EIA). The morphology of the COCs and maturation rates of the oocytes were then evaluated using two comparisons. In first comparison, the left and right ovaries obtained from an individual cow were considered as a pair, with each pair being divided into two groups depending on the presence or absence of an E2 dominant or P4 dominant cystic follicle in one or another of the ovaries: E2 dominant cows; and P4 dominant cows. Oocytes collected from the ovaries of cyclic cows at follicular, luteal and post-ovulatory stages served as controls. The oocyte recovery rates, oocyte morphologies and oocyte maturation rates were independent of the presence or absence of a coexisting cystic follicle, or its steroid hormone classification or concentration. In the second comparison, each ovary was consider individually and divided into one of the two classes, depending on the presence or absence of a cystic follicle. Those ovaries with cystic follicles were then divided into three subclasses on the basis of E2 and P4 concentrations in the cystic follicular fluids: P4 dominant (P4/E2 ratio > 1); E2 dominant (P4/E2 ratio < 1); and both P4 and E2 dominant follicles present. The numbers of oocytes obtained from an ovary, their morphology and their maturation rates were not significantly different in the presence or absence of a coexisting cystic follicle. Moreover, the number of the oocytes aspirated from an ovary, their morphology and their maturation rates in small follicles coexisting with P4 dominant, E2 dominant and both P4 and E2 dominant cystic follicles were also not different. These results suggested that neither the presence of a cystic follicle in a cow's ovary nor the cyst's steroid hormone concentrations affected the oocyte recovery rate, oocyte morphology and maturation rates of the coexisting small follicles.