Delayed follicular development and ovulation following inhibition of FSH with equine follicular fluid in the mare

In two experiments, PGF(2alpha) was given to all mares on Day 10 (ovulation = Day 0). In experiment 1, mares received either whole follicular fluid or saline i.v. every 12 hours on Days 10 to 14. Experiment 2 was similar to experiment 1, except the follicular fluid was extracted with charcoal to remove steroids. Analysis of the FSH data for Days 10 to 21 indicated an effect of treatment (P<0.08) with whole follicular fluid, but not with charcoal-extracted follicular fluid. However, there was an effect of day (P<0.05) and an interaction (P<0.01) of treatment with day for both experiments. The interaction of treatment with day seemed primarily due to a marked post-treatment increase in FSH concentrations between Days 15 and 17 for mares treated with either whole follicular fluid or charcoal-extracted follicular fluid. Analysis of the diameter of the largest follicle for Days 10 to 18 indicated a main effect of treatment (P<0.05) and day (P<0.05) and an interaction (P<0.05) of treatment with day for both experiments. The interaction of treatment with day was attributable to the inhibition of follicular growth by Day 14 for mares treated with whole follicular fluid and by Day 15 for mares treated with charcoal-extracted follicular fluid. The length of the interovulatory interval was longer (P<0.05) in the treated group than in controls for both experiments. Results indicated that equine follicular fluid contained a proteinaceous substance that suppressed circulating concentration of FSH. The inhibited follicular growth and the delay in ovulation were attributed to the reduced concentrations of circulating FSH.