Peaks in serum concentrations of FSH (outlined with shading) and their associated emerging follicle waves in cyclic Western White Face ewes treated for 10 d, from Day 4 after ovulation (Day 4–14; indicated by an open rectangular box on the X-axis) with silastic rubber implants (s.c) containing 10% progesterone (bottom panel; n = 6) and sham operated control ewes (top panel; n = 6). Data were normalized to the day of ovulation (Day 0) in all ewes. Concentrations of FSH and follicle diameters are expressed as mean ± S.E.M. The average curves representing the growth, static and regression phases of all ewes in a group were normalized for each follicle wave to the mean day of wave emergence (indicated by the arrows; ). All FSH peaks for all ewes are shown normalized to the mean day of occurrence of the apex of the FSH peak for each wave. Although most follicular waves emerge at the zenith of the FSH peak, emergence can occur one day before or after the zenith of the FSH peak. For every FSH peak, serum concentration profiles were delimited by the encompassing nadirs of the FSH concentrations (hence the overlap of the data for adjacent peaks in some cases).