Ovarian sensitivity of the prepubertal ewe to exogenous gonadotropins

Ovulatory response of prepubertal ewe lambs of Booroola Merino x Rambouillet (F+) and Rambouillet (++) breeding was compared after administration of 500 IU PMSG, 750 IU hCG, a combination of PMSG and hCG (500 IU PMSG followed by 250 IU hCG), 4, 8, 20, 30 or 40 mg of ovine pituitary extract or 12 mg of FSH-p.The distribution of number of ovulations per ewe was found not to be significantly different between genotypes after administration of hCG, PMSG and hCG combination or 4, 8 or 30 mg of ovine pituitary extract. Significant differences between genotypes were observed after administration of 500 IU PMSG, 20 and 40 mg of pituitary extract and 12 mg of FSH-p. If 2 or more induced ovulations was selected as the criterion for presence of the "F" gene, F+ ewes were correctly classified 64.3% of the time after PMSG, 65.4% of the time after 20 or 40 mg of ovine pituitary extract and 68.2% of the time after FSH-p treatments, and ++ ewes were correctly classified 76.5%, 96.2% and 61.5% of the time, respectively. If 3 or more induced ovulations was the criterion, PMSG resulted in 37.3%, 20 or 40 mg of ovine pituitary extract resulted in 23.1% and FSH-p would result in 59.1% of F+ ewes identified correctly, and ++ ewes were correctly classified 97.1%, 100% and 76.9% of the time, respectively.Blood plasma FSH levels of the prepubertal ewe lambs from (F+) and (++) genotypes were determined by radioimmunoassay procedures to determine if there were any differences between genotypes at ages of 30, 45 and 60 days. Data from 1988 indicated that the F+ genotype had significantly higher basal FSH levels at 30 days of age than the ++ genotype. Both 1989 and 1990 data, however, showed no differences between genotypes.Phenotypic correlations between FSH concentrations, number of induced ovulations, number of natural ovulations and litter size failed to reveal any strong relationships which would allow the predication of performance for adult reproductive traits from the prepubertal traits in individual animals. Bodin et al. (1988), stated that phenotypic correlation between prolificacy and FSH levels was positive but not significant.U of I OnlyETDs are only available to UIUC Users without author permissio