Follicular waves are associated with transient fluctuations in FSH but notoestradiol or inhibin-A concentrations in anoestrous ewes

The aim was to examine statistically the changes among days in the numbers of follicles relative to tire growth of large follicles to test the hypothe sis that follicular development occurs in a wave-like fashion in anoestrous ewes. The relationships among the patterns of circulating concentrations o f FSH, oestradiol and inhibin-A and the pattern of follicular growth as wel l as relationships among follicular fluid steroid and inhibin-A concentrati ons were also studied. The ovaries of 21 ewes were examined daily using tra nsrectal ultrasonography for 14 days and blood samples were collected every 8 h for 9 days. Five ewes were overiectomized on the last day of ultrasoun d scanning. One to three identified follicles (a cohort) emerged every 2 to 5 days (mean 2.9 (s.e. 0.2) days) in individual ewes. The numbers of 4 and 5 mm follicles were fewest (P < 0.05) before and greatest (P < 0.05) 7 day after cohort emergence. This change in the numbers of follicles indicates a wave-like pattern of follicular growth. FSH concentrations were greatest (P < 0.05) on the day before wave emergence and lowest (P < 0.05) on the da y of wave emergence. Peripheral concentrations of oestradiol and inhibin-A did not fluctuate (P < 0.05) in association with the emergence of follicula r waves. The follicles that were collected at ovariectomy originated from o ne of three different waves. Oestradiol and inhibin-A concentrations in fol licular fluid and the oestradiol-to-progesterone ratio were not different a mong tile largest follicles of successive waves, when follicles were collec ted at the same time, indicating that new waves of follicles developed befo re the demise of old waves. In conclusion, waves of follicles emerged about every 3 days in anoestrous ewes (defined as significant changes in numbers of follicles) and were associated with fluctuations in FSH concentrations but not peripheral oestradiol or inhibin-A concentrations. New follicular w aves also emerged in the presence of steroidogenically active (positive oes tradiol-ro-progesterone ratio), inhibin-A producing follicles from a previo us wave suggesting that follicles do not exert functional dominance during the non-breeding season.