Systemic and intraovarian effects of corpus luteum on follicular dynamics during estrous cycle in hair breed sheep

The present study aimed to determine systemic and local effects of corpora lutea (CL), on follicular dynamics throughout the estrous cycle. All follicles ≥2 mm and CL were assessed by daily transrectal ultrasonography in 12 West African ewes. Blood samples were collected to determine plasma concentration of progesterone. Fifteen estrous cycles were evaluated with a mean interovulatory interval of 16.8 ± 0.2 days. Two (13.3%), 10 (66.7%) and 3 (20%) of the estrous cycles had 2, 3 and 4 waves of follicular development, respectively. In sheep with three waves of follicular development, both the length of growing phase and the growth rate of dominant follicles from midluteal wave II were diminished (3.4 ± 0.3 days, P < 0.0001, and 0.4 ± 0.1 mm/day, P < 0.01, respectively) when compared to follicles from early luteal phase (wave I, 4.1 ± 0.2 days, and 0.7 ± 0.1 mm/day) or late luteal phase (wave III, 6.3 ± 0.4 mm and 0.6 ± 0.1 mm/day). The diameter of the dominant follicle was smaller during the midluteal phase (3.9 ± 0.1 mm, P < 0.0001) than in the early and late luteal phase (5.0 ± 0.2 and 5.7 ± 0.2 mm; respectively). The effect of the dominant follicle was less during midluteal phase, because number of accompanying smaller follicles was fewer (P < 0.01) in waves I and III (6.3 ± 0.9 compared with 3.4 ± 0.8 and 2.3 ± 0.7). The number of follicles was also different between ovaries that had CL and those that did not. The total number of large follicles during the luteal phase was less in ovaries with CL (0.9 ± 0.5 compared with 2.7 ± 0.3; P < 0.01), as was the mean daily number of both large (0.1 ± 0.02 compared with 0.2 ± 0.02; P < 0.001) and total number of follicles ≥2 mm (2.5 ± 0.1 compared with 3.3 ± 0.1; P < 0.01). Current results indicate that the presence of a functional CL may exert both systemic and local effects on the population of follicles, affecting the dominance exerted by large follicles.