Comparative efficacy of two immunocontraceptive vaccines.

As part of our research program to develop immunocontraception as a wildlife management tool, we compared the physiological responses of wild Norway rats (Rattus norvegicus) to two immunocontraceptive vaccines; one involved mouse zona pellucida peptide (MZPP); the other involved gonadotropin releasing hormone (GnRH). Efficacy was monitored by immune, hormonal, and natality responses. Both vaccines were effective, but GnRH was much more effective (100% sterility of both sexes vs. 50% sterility of MZPP-treated females). Breeding success of control rats was 88% with litters of 5-9 pups; breeding success of MZPP rats was 50% with litters of 2-8; GnRH rats produced no young. In GnRH-treated male rats monitored for up to 17 months, testosterone was nondetectable and testes were atrophied to about 10% of their original volume for 10-13 months. There were no notable differences in mortality or body weights among groups, and, with the exception of testicular regression, there were no changes in general appearance. The GnRH vaccine is potentially a good rat reproductive control agent that may be effective over the normal lifespan of a rat under natural conditions in the wild.