Effects of a dominant follicle on ovarian follicular dynamics during the oestrous cycle in heifers

Abstract

Summary. Two hypotheses were tested: (1) a dominant follicle causes regression of its subordinate follicles, and (2) a dominant follicle during its growing phase suppresses the emergence of the next wave. Cyclic heifers were randomly assigned to one of four groups (6 heifers/group): cauterization of the dominant follicle of Wave 1 or sham surgery (control) on Day 3 or Day 5 (day of ovulation = Day 0). Ultrasonic monitoring of individually identified follicles was done once daily throughout the interovulatory interval. The onset of regression (decreasing diameter) of the largest subordinate follicle of Wave 1 was delayed (P < 0·01) by cauterization of the dominant follicle of Wave 1 on Day 3 compared to controls (mean onset of regression, Days 10·8 ± 2·1 vs 4·3 ± 0·4). Cauterization of the dominant follicle of Wave 1 on Days 3 or 5 caused early emergence (P < 0·01) of Wave 2 when compared to controls (Day-3 groups: Days 5·5 ± 0·4 vs 9·6 ± 0·7; Day-5 groups: Days 7·0 ± 0·3 vs 9·1 ± 0·4). The results supported the two hypotheses. In addition, cauterization of the dominant follicle of Wave 1 on Days 3 or 5 increased the incidence of 3-wave interovulatory intervals. Keywords: ovary; follicles; follicular waves; cattle; cauterization