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

摘要

Daily transrectal ultrasound scanning and twice-daily blood sampling were used to monitor the temporal relationships between FSH concentrations and follicle development during complete interovulatory intervals for ewes in which the ovulation rate ineach of the 2 previous years was high (>=3; n = 6) or low (<=2; n = 6). Follicles >=5 mm were used to define a follicular wave and were traced retrospectively to 3 mm (emergence). The hypothesis that FSH surges (identified with a computer program) and follicular waves (retrospectively determined based on ultrasound scanning) are temporally associated was supported in both groups by the emergence of an anovulatory or ovulatory follicular wave near the peak of an FSH surge. There was also a significant increase in FSH concentrations before and a significant decrease after follicular-wave emergence in both groups independent of the identification of FSH surges. Ewes with a high ovulation rate had smaller follicles (anovulatory and ovulatory) and more ovulations, but the 2 groups were similar in the number of ovulatory follicular waves and associated FSH surges, number and characteristics of the FSH surges, and mean FSH concentrations per interovulatory interval. Surges of FSH were periodic (every 3 or 4 days) regardless of the ovulation-rate group or follicle response. In ewes with a low ovulation rate, the non-ovulatory FSH surges were most frequently associated with emergence of detected anovulatory follicular waves. In ewes with a high ovulation rate,more FSH surges were not associated with a detected follicular wave, probably because the largest follicle was <5 mm. It is concluded that the factors resulting in a high ovulation rate are not exerted through circulatory patterns or concentrations of FSH but involve a shorter growth phase and smaller maximal diameter of follicles.