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 monoclon al antibody purified inhibin (bMPI) obtained by immunochromatography f rom bovine follicular fluid or with adjuvant alone (control). Antibodi es in the plasma of the lambs immunized with the inhibin preparations bound to iodinated 31 kDa bovine inhibin. Binding was minimal after th e 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 activit y (as hoggets) was advanced (P<0.05) by 17 days in lambs immunized wit h 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 anim als (1.27+/-0.15) but not in the bMPI-treated lambs (1.40+/-0.16). Aft er 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 th ose in the control group (1.15+/-0.08). There were no effects of immun ization on plasma concentrations of either follicle stimulating hormon e (FSH) or luteinizing hormone (LH), The initial smaller response seen with the bMPI may be due to either the presence of compounds other th an inhibin in such preparations or the small absolute amount of inhibi n injected. The latter seems more probable since these animals did res pond to a booster immunization as hoggets to obtain an ovulation rate similar to that of the recombinant inhibin-immunized lambs. Immunizati on had no effect on growth rate, length of oestrous cycle, or time fro m injection of prostaglandin analogue to onset of oestrus. In conclusi on, immunization of ewe lambs with rec inhibin increased ovulation rat e and advanced the onset of puberty.