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

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 ovaries1and adrenals1, is quantitatively the major steroid secreted by the ovary before ovulation in several species2and 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 oestrogens4a direct hormonal action has only been demonstrated in the female rhesus monkeys5where 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.