T. Oshea et al., ACTIVE IMMUNIZATION OF MERINO EWE LAMBS WITH RECOMBINANT BOVINE ALPHA-INHIBIN ADVANCES PUBERTY AND INCREASES OVULATION RATE, Reproduction, fertility and development, 5(2), 1993, pp. 173-180
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.