Abstract

Ewes that are heterozygous (I+) carriers of the Inverdale gene (FecX) have increased ovulation rate, whereas ewes that are homozygous (II) for the gene are infertile and have 'streak' ovaries in which normal follicle development does not occur. A proportion of ewes with streak ovaries develop structures that have some characteristics of ovarian tumours. We have monitored the growth of ovarian structures and (c) assess the effectiveness of using hormone concentrations to identify the genotype of individual ewe lambs. No differences in hormone secretion related to differences in ovulation rate were evident between I+ and non-carrier (++) Inverdale ewes (mean ovulation rates 3.1+/-0.22 ng/ml) nor inhibin concentrations of gonadotrophins were consistently elevated (FSH 16.9+/-1.8 ng/ml; LH 4.5+/-0.5 ng/ml; N+14) and were comparable to those observed in ovariectomised ewes. In contrast, inhibin was always undetectable (<3.0I.U./ml). These patterns of hormone secretion often change markedly when ovarian structures develop, with inhibin concentrations increasing acutely, which in turn causes FSH levels to fall. To assess the potential of using these differences to identify II genotype, Inverdale ewe lambs were blood-sampled at two, five or seven months of age. Over 95% of II Inverdale ewe lambs had genotype assigned correctly (confirmed by laparoscopy) on the basis of plasma FSH concentrations alone.

BJ, McLeod, SE Kyle, MR Ramsay, and TR Manley

Proceedings of the New Zealand Society of Animal Production, Volume 55, , 304-306, 1995