Abstract
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 (lmg 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 >>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.
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