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
1998
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 greater than or equal to 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.
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