Development of an Antifertility Vaccine for Pets Based on Active Immunization against Luteinizing Hormone-Releasing Hormone1

Male dogs and cats were immunized against LHRH in order to evaluate the feasibility of an immunological approach to pet contraception. In the first study, dogs were immunized with 100, 500, or 2500 micrograms of LHRH conjugated to tetanus toxoid. A significant decline in serum testosterone (T) levels was observed in all immunized dogs, reaching castration levels in some animals by Week 4 and remaining suppressed in all the immunized dogs through the course of the study. Testicular histology suggested arrest of spermatogenesis (infertility). The effects of "immunological castration" were reversible (study 2): steroidogenesis suppressed by "immunological castration" was restored as antibody titers declined. Effective antibodies were rapidly reinduced in dogs by a single injection of LHRH1-TT. In contrast, the level of antibodies induced in male cats (study 3) was not sufficient for "immunological castration." The conclusion was that active immunization against LHRH could provide a cost-effective, nonsurgical, reversible means to control the fertility of companion animals.