Superstimulation of ovarian follicular growth with fsh, oocyte recovery, and embryo production from zebu (bos indicus) calves: Effects of treatment with a gnrh agonist or antagonist

Abstract

The capacity of heifer calves of a late sexually maturing Zebu (Bos indicus) genotype to respond to superstimulation with FSH at a young age and in vitro oocyte development were examined. Some calves were treated with a GnRH agonist (deslorelin) or antagonist (cetrorelix) to determine whether altering plasma concentrations of LH would influence follicular responses to FSH and oocyte developmental competency. Brahman calves (3-mo-old; 140±3 kg) were randomly assigned to 3 groups: control (n=10); deslorelin treatment from Day -8 to 3 (n=10); and cetrorelix treatment from Day -3 to 2 (n=10). All calves were stimulated with FSH from Day 0 to 2, and were ovariectomized on Day 3 to determine follicular responses to FSH and to recover oocytes for in vitro procedures. Before treatment with FSH, heifers receiving deslorelin had greater (P<0.001) plasma LH (0.30±0.01 ng/ml) than control heifers (0.17±0.02 ng/ml), while plasma LH was reduced (P<0.05) in heifers treated with cetrorelix (0.13±0.01 ng/ml). Control heifers had a surge release of LH during treatment with FSH, but this did not occur in heifers treated with deslorelin or cetrorelix. All heifers had large numbers of follicles ≥ 2 mm (approximately 60 follicles) after superstimulation with FSH, and there were no differences (P>0.10) between groups. Total numbers of oocytes recovered and cultured also did not differ (P>0.05) for control heifers and heifers treated with deslorelin or cetrorelix. Fertilization and cleavage rates were similar for the 3 groups, and developmental rates to blastocysts were also similar. Zebu heifers respond well to superstimulation with FSH at a young age, and their oocytes are developmentally competent.