Increasing ovulation rate in sheep by active immunization against an ovarian steroid androstenedione

Abstract

ALTHOUGH low rates of ovulation constitute a major limitation to increased productivity of sheep and cattle little is known about the mechanisms that control ovulation either within or among species. Androstenedionem a week androgen secreted by ovaries¹ and adrenals¹, is quantitatively the major steroid secreted by the ovary before ovulation in several species² and as such it might have a role in determining ovulation rate; it is also an important precursor for the biosynthesis of oestrogens, by the ovary³. Although androstenedione can act as a prehormone by virtue of its peripheral metabolism to oestrogens⁴ a direct hormonal action has only been demonstrated in the female rhesus monkeys⁵ where it seems to be important for sexual behaviour. We report here that by actively immunizing sheep against androstenedione a slight but significant increase in ovulation rate can be induced.