Follicular characteristics and luteal development after follicle-stimulating hormone induced multiple ovulations in heifers.

A protocol based on small doses of FSH was examined for the induction of double or triple (multiple) ovulations in cattle. Ovulation rate, follicular characteristics, and luteal responses were determined. In Exp. 1, three groups of estrous-synchronized, cyclic Holstein heifers were treated once daily, on d 3 to 6 of the cycle, with a FSH product (Folltropin-V): large FSH dose (total of 150 mg; n=18), medium FSH dose (total of 130 mg, n=12), and small FSH dose (total of 80 mg; n=7). Controls received saline (n=6). Prostaglandin F(2α) was injected on d 6, ultrasound-guided aspiration of surplus follicles (if needed) was performed on d 7, and GnRH was injected on d 8 to induce ovulation. The large FSH dose induced growth of more (2.6±0.3, P<0.05) large follicles than controls on d 8; medium and small FSH doses insufficiently stimulated growth of <2 large follicles. Ovulation rates were determined in subgroups of heifers (n=10, 13, 4, and 6, respectively). The large FSH dose induced greater rates (P<0.01) of mostly double and triple ovulations (90% multiple ovulations, 70% double ovulations), most of which (89%) were bilateral, with only 2 out of 10 heifers requiring aspiration of surplus follicles. Medium and small FSH doses induced fewer multiple ovulations (38% and 25%, respectively). Estradiol concentrations on d 8 did not differ among treatments, but the concentration per large follicle in controls was greater (P<0.05) than in FSH treatments. Mean corpus luteum (CL) volume in single-ovulation controls was greater (P<0.05) than that of multiple ovulations in the large FSH group and total CL volume and progesterone concentrations were numerically greater in multiple ovulations. In Exp. 2, the characteristics of follicles aspirated on d 7 from large FSH (n=11) and control heifers (n=10) were compared. Based on estradiol-to-progesterone ratio, 57% of the large FSH-treated follicles were classified as codominant/healthy follicles and 43% as subordinate/early atretic. Although concentrations of estradiol and androstenedione in FSH-treated codominant follicles were less (P<0.05) than in controls, estradiol-to-progesterone ratio indicated that those follicles were steroidogenically active. Finely tuned small doses of FSH administered during the first follicular wave can induce a large incidence of double/triple, mainly bilateral, ovulations in cattle, which may serve as a basis for treatment aimed at promoting twinning in beef cattle.