Discussion

Abstract

Seasonal anestrus in sheep is characterized by an LH episode frequency which is below that necessary for the induction of the final phases of follicle growth. In some breeds the restoration of this inadequacy by appropriate therapy with either purified LH or GnRH will promote ovulation. However, in “deeply” anestrous breeds it is necessary to use a combination of FSH and LH. Such differences indicate that the endocrinology of seasonal anestrus is not a consistent phenomenon and depth of anestrus may relate to differences in the extent of early follicle development. However, the ovaries are not quiescent during the non-breeding season, even in the very seasonal breeds. Indeed, follicle recruitment up to a fairly advanced stage of development is present. Genetic influences are manifest, in that the mechanisms controlling ovulation rate still appear to be present even during seasonal anestrus.