Role of increased estradiol on altering the follicle diameters and gonadotropin concentrations that have been reported for double-ovulating heifers

Abstract During the preovulatory period in heifers that ovulate from two compared to one follicle, circulating concentrations of estradiol-17β (E2) are greater, diameter of follicles and concentration of FSH are reduced, and the LH surge occurs sooner. The effect of increased E2 on the reported characteristics of double ovulation was studied by treating heifers with 0.07mg E2, 0.09mg E2, or vehicle in four treatments at 6-h intervals ( n =6 heifers/group), beginning at the time of expected follicle deviation (largest follicle, 8.5mm). There were no significant differences on follicle diameters or hormone concentrations between the 0.07 and 0.09mg E2 groups, and heifers were combined into one E2 group ( n =12). The E2 treatments induced concomitant preovulatory surges in LH and FSH at 34.0±2.6h after first treatment, compared to 57.6±4.5h in the vehicle group ( P P