COUNTERACTION OF THE FOLLICULAR INHIBITORY EFFECT OF FOLLICULAR-FLUID BY ADMINISTRATION OF FSH IN HEIFERS

The hypothesis that a factor in follicular fluid suppresses follicular growth independently of reduced systematic FSH concentrations in cattle was tested in a 2 x 2 factorial designed experiment (n = 5 heifers group(-1)). Treatment, at 12-h intervals, began on day 0 (ovulation) and ended on day 1. Mean (+/- SEM) diameter of the largest follicle, averaged over all days, and maximum diameter attained on days 0-9 was smaller (P < 0.05) in heifers given follicular fluid (8.4 +/- 0.4 and 12.4 +/- 1.0 mm, respectively) than in heifers given either saline (10.3 +/- 0.6 and 14.8 +/- 0.6 mm) or follicular fluid plus FSH (10.7 +/- 0.6 and 16.8 +/- 0.4 mm). The day-to-day mean diameter profiles of both the largest and second-largest follicles for days 0-9 were similar among heifers given saline, follicular fluid plus FSH, and FSH alone, whereas the follicle profile was reduced in heifers given follicular fluid alone. Mean follicle diameters were smaller (P < 0.05) on days 4-9 and days 2 and 5 in heifers given follicular fluid than in heifers given either saline or follicular fluid plus FSH. The results did not support the hypothesis, since exogenous FSH overrode follicular inhibition induced by follicular-fluid treatment.