Ovarian Response and Hormonal Profiles in Heifers After Immunization and Re-immunization Against Inhibin .ALPHA.-Subunit.

Abstract

To explore a strategy for superovulation in heifers, effects of immunization and re-immunization of Japanese beef heifers against inhibin on ovarian response and hormonal profiles were investigated. On day 9 of the estrous cycle (day 0=day of estrus), ten heifers were primary injected intramuscularly (i.m.) either with inhibin vaccine (recombinant ovine inhibin α-subunit in oil emulsion, 125 μg/ml) or a placebo (Montanide:Marcol adjutant alone) followed by two booster injections at one estrous cycle intervals (immunized group). One year later, 3 injections of inhibin vaccine were given the same as in the first year (re-immunized group). Inhibin antibody titers in plasma of immunized heifers increased after the second injection of inhibin vaccine and in 3 out of 5 immunized heifers and multiple-ovulation (2.4 ± 0.6, n=5) was induced after the third injection. On the other hand, in the re-immunized heifers, the plasma inhibin antibody titers increased sharply after the first injection of inhibin vaccine and in 4 out of 5 re-immunized heifers multiple ovulation (4.4 ± 1.1, n=5) was induced after the first injection of inhibin vaccine. In all re-immunized heifers multiple-ovulation was induced after the third injection of inhibin vaccine (5.0 ± 1.1, n=5). The results also showed that the ovulation rates were positively correlated to circulating inhibin antibody titers and plasma levels of FSH. These results confirmed that active immunization against inhibin α-subunit induced multiple ovulation mainly by attenuation of the suppressive effect of inhibin on FSH secretion in heifers and indicated that re-immunization against inhibin was a good way to induce multiple-ovulation in cattle.