Effects of active immunization against androstenedione or oestrone on oestrus, ovulation and lambing in Merino ewes

Abstract

Merino ewes were immunized against bovine serum albumin (BSA), or oestrone or androstenedione, conjugated to BSA. Immunization against oestrone and androstenedione elevated the mean number of ovulations per ewe ovulating (ovulation rate) from 1.2 to 1.5 and 2.3, respectively. The higher ovulation rate was not reflected in more lambs born per ewe lambing (1.12-1 .I 6 for all groups). The frequency of ovulation and oestrus was depressed in ewes immune to oestrone, and there was a high frequency of abnormalities in the reproductive tract. These effects of immunization were not as frequent in ewes immune to androstenedione. There was no relation between titre and any measure of reproductive performance. The use of immunization against ovarian steroids to improve the reproductive efficiency of commercial flocks is not justified without further investigation.