Effects of active immunization of the ram and bull against luteinizing hormone

Active immunization of ram lambs and bull calves against highly purified LH results in the production of antibodies which bind radiolabeled ovine LH. Antibody titers were not dependent upon the dose (0.1 or 1.0 mg) of antigen given but were found to be greater when the antigen consisted of LH conjugated to a carrier protein; in this case human serum globulin (hSG). The presence of LH antibodies in ram sera seemed of little consequence. The presence of antibodies in sera of immunized bulls, however, appeared to neutralize endogenous LH sufficiently to suppress serum testosterone and reduce testicular size. Androgen deficiency, produced by immunization against oLH-hSG, resulted in atrophy of the testes, seminal vesicles and epithelial cells lining both epididymides and seminal vesicles. Reduced weight gain and lack of development of the secondary sexual characteristics were at levels expected of surgical castrates (steers). In summary, active immunization of young beef bulls against LH and in particular, oLH-hSG, results in a castration-like response which has been compared with that achieved in other species by luteinizing hormone releasing hormone (LHRH) immunocastration. The success of LH immunocastration in field trials with young bulls and investigations aimed toward reversibility are yet to be determined.