Active immunization against follistatin and its effect on FSH, follicle development and superovulation in heifers

Ovaries of heifers were examined daily by transrectal ultrasonography for one interovulatory interval before initiation of immunizations (control cycle, n = 14), and again after the fifth immunization with a sham-vaccine (Freund's adjuvant only; n = 7) or a recombinant porcine follistatin-vaccine (1 mg per vaccination; n = 7) to study the effect of follistatin on follicle dynamics. After the fifth immunization, 4 heifers had a follistatin antibody titer of > or = 1:3200, while the remaining 3 heifers had a titer of only 1:400. At wave emergence, the total number of follicles and the number of small follicles (3 to 5 mm) were higher (P < 0.05) in the follistatin group than in the control and sham groups. In addition, high-titer heifers had a greater (P < 0.05) number of follicles (total and small) per day than low-titer heifers. Plasma concentration of FSH remained unchanged after sham- or follistatin-immunization. Sham- and follistatin-vaccinated heifers were then given half the standard superovulatory dose of Folltropin (200 mg of FSH) 14 d after the sixth immunization. More ovulations were detected in follistatin- (10.9 +/- 2.4) than sham- (5.0 +/- 0.8) vaccinated heifers (P < 0.05). Moreover, heifers with a high titer had more ovulations (P < 0.02) than heifers with a low titer (15.0 +/- 2.5 vs 5.3 +/- 1.2). The number of ova-embryos classified as fertilized:unfertilized and transferable:discarded, and quality of the embryos were similar between sham and follistatin groups. By 80 d after the last immunization, when antibody titers were undetectable in the follistatin group, there was no difference in superovulatory response between sham (6.7 +/- 1.6) and follistatin (7.6 +/- 1.6) groups. In summary, follistatin immunization was associated with an increase in the number of small follicles at the time of wave emergence and a greater response to superovulatory treatment. The results suggest that effects of follistatin on follicular dynamics were not mediated through changes in pituitary secretion of FSH.