The effect of different doses of estradiol benzoate on follicle development and twin birth in beef cattle with induced superovulation

Abstract. The aim of this study was to evaluate the effect of different doses of estradiol benzoate (EB) on inhibiting the development of non-dominant follicles and inducing twin calves in beef heifers. Beef heifers were synchronized using estradiol plus progesterone (P4), and superovulation was induced using a small-dose follicle-stimulating hormone (FSH) protocol. From day 6.5 to day 7.5, every heifer was treated with 0, 0.1, 0.2, or 0.5 mg EB three times at 12 h intervals to eliminate excess dominant follicles. The diameters of the two largest follicles (F1 and F2) continually increased from day 3.5 to day 10. However, the growth rate was constrained by exogenous EB, and the degree of suppression was greatest in the 0.5 mg EB treatment compared with other treatments. As a result, the number of large follicles (≥10 mm) decreased as the EB dose increased. Compared with the control treatment, the incidence of animals experiencing triple ovulation was significantly lower in the 0.5 mg EB treatment; however, the single-ovulation rate showed the inverse. This study demonstrated that 0.2 mg EB could modulate the development of two to three co-dominant follicles after a small-dose FSH treatment. The number of twin births was higher in the 0.2 mg EB treatment.