Ovarian Function in the Cycling Cow: Relationship between Gonadotropin Binding to Theca and Granulosa and Steroidogenesis in Individual Follicles2

Abstract

Thirty-six Angus and Angus crossbred cows were used in a 3 × 2 × 2 factorial experiment designed to determine the effects of stage of the estrous cycle (day 6, 12 or 18), a long term with a single ovary (2 years) and side of previous ovulation or remaining ovary on the development of large ovarian follicles (LF; diameter >8 mm). Follicular fluid estradiol-17)β (FFE) concentration, localization of gonado-tropin binding sites and granulosa cell condition were determined for each LF by radio-immunoassay, autoradiography and histological examination, respectively. No side differences were noted. However, the sample was biased by the use of equal numbers of left and right side ovulators. Compared to intact controls, one-ovary cows showed 100% compensation of LF development. Eighty-five percent of the LF studied bound follicle stimulating hormone (FSH) in the granulosa and human chorionic gonadotropin (hCG) in the theca. Thirty-eight percent also bound hCG in the granulosa. Both binding patterns were found on all days studied. Atretic follicles had lower (P<.05) FFE concentrations than healthy follicles (r = -.59). The number of LF per cow increased (P<.05) from day 6 (1.3) to days 12 (1.8) and 18 (2.1). Conversely, their FFE content per cow decreased (P<.05) from 109 ng/cow on day 6 to 20 ng on day 12 and 34 ng on day 18. The data suggested the emergence of two LF classes on day 18, one pre-ovulatory, with exceptionally high FFE levels, the other atretic or becoming atretic, with low FFE levels. Copyright © 1981. American Society of Animal Science . Copyright 1981 by American Society of Animal Science.