Active immunization of Merino ewe lambs with recombinant bovine alpha inhibin advances puberty and increases ovulation rate.

Ewe lambs (n = 24-25) were immunized at 3, 7 and 15 weeks of age with recombinant bovine alpha-inhibin (rec inhibin) or with bovine monoclonal antibody purified inhibin (bMPI) obtained by immunochromatography from bovine follicular fluid or with adjuvant alone (control). Antibodies in the plasma of the lambs immunized with the inhibin preparations bound to iodinated 31 kDa bovine inhibin. Binding was minimal after the primary immunization, increased after each booster immunization and remained elevated until at least 45 weeks of age (29% for rec inhibin and 11% for bMPI). Of the group treated with rec inhibin, 10 ovulated as lambs (control 0/22; bMPI 3/21) and onset of overt oestrous activity (as hoggets) was advanced (P < 0.05) by 17 days in lambs immunized with rec inhibin. As hoggets, the ovulation rate was greater (P < 0.01) in the rec inhibin immunized lambs (4.41 +/- 0.67) than in the control animals (1.27 +/- 0.15) but not in the bMPI-treated lambs (1.40 +/- 0.16). After a further immunization at 17 months of age, however, ovulation rate increased (P < 0.01) in the bMPI-immunized group (3.40 +/- 0.47) but was unchanged in the lambs immunized with rec inhibin (2.80 +/- 0.52) and those in the control group (1.15 +/- 0.08). There were no effects of immunization on plasma concentrations of either follicle stimulating hormone (FSH) or luteinizing hormone (LH). The initial smaller response seen with the bMPI may be due to either the presence of compounds other than inhibin in such preparations or the small absolute amount of inhibin injected.(ABSTRACT TRUNCATED AT 250 WORDS)