Follicular and fsh dynamics in ewes with a history of high and low ovulation rates

Daily transrectal ultrasound scanning and twice-daily blood sampling were u sed to monitor the temporal relationships between FSH concentrations and fo llicle development during complete interovulatory intervals for ewes in whi ch the ovulation rate in each of the 2 previous years was high or low (grea ter than or equal to 3 and less than or equal to 2 ovulations, respectively ). Follicles that reached greater than or equal to 5 mm were used to define a follicular wave and were tracked retrospectively to 3 mm (emergence). Th e hypothesis that FSH surges (identified with a computer program) and folli cular waves (retrospectively determined based on ultrasound scanning) are t emporally associated was supported in both groups by the emergence of an an ovulatory or ovulatory follicular wave near the peak of an FSH surge. Furth er support for the hypothesis was a significant increase in FSH concentrati ons before and a significant decrease after follicular-wave emergence in bo th groups independent of the identification of FSH surges. Ewes with a hist ory of high ovulation rates had smaller follicles (anovulatory and ovulator y) and more ovulations, but the 2 groups were similar in the number of ovul atory follicular waves and associated FSH surges, number and characteristic s of the FSH surges, and mean FSH concentrations per interovulatory interva l. Surges of FSH were periodic (every 3 or 4 d) regardless of the ovulation -rate group or follicle response. In ewes with a low ovulation rate, the no novulatory FSH surges were most frequently associated with emergence of det ected anovulatory follicular waves. In ewes with a high ovulation rate, mor e FSH surges were not associated with a detected follicular wave, as define d, presumably because the largest follicle did not reach 5 mm. The results indicated that the factors resulting in a high ovulation rate were not exer ted through circulatory patterns or concentrations of FSH but involved a sh orter growth phase and smaller maximal diameter of follicles. (C) 1999 by E lsevier Science Inc.