Active immunisation of Romney ewes with an androstenedione–protein conjugate

Publisher Website
Google Scholar
Abstract
Romney ewes were immunized on 1 occasion with androstenedione-6-hemisuccinate-bovine serum albumin during mid-anestrus (Dec.). The onset of seasonal estrous activity, the number of animals displaying estrous behavior and the number of ovulations per ewe were recorded during the following breeding season. The results were compared with those from untreated (control) animals and from animals treated with pregnant mare serum gonadotrophin (PMSG). The immunized animals showed a small but highly significant increase (P < 0.001) in the mean ovulation rate (1.43 ovulations/ewe) relative to control (1.08 ovulations/ewe). The increased ovulation rate in the immunized ewes was comparable with that achieved in the animals treated with PMSG (1.37 ovulations/ewe). None of the animals that were immunized with the androstenedione-protein conjugate ovulated more than 2 follicles, and all but 1 showed estrous activity. Many of the animals with low antibody titers against androstenedione had an increase in ovulation rate (11 ewes with titers < 1:5000 had 1.55 ovulation/ewe); those with high antibody titers more commonly had low ovulation rates (11 ewes with titers > 1:5000 had 1.27 ovulations/ewe). A possible interference in behavioral estrous activity appeared to be associated with high antibody titers. If further studies can show an increased number of live births per ewe mated, a single-injection procedure with an androstenedione-protein conjugate may be of practical importance in enhancing the fecundity of New Zealand Romney ewes.