Avian contraception is a nonlethal management tool that can be utilized for managing wild species associated with damage, or to manage reproduction in captive populations. Because management situations vary with respect to the management goal, species involved, location, and nontarget hazards, it is necessary to develop multiple contraceptive tools to allow management flexibility.
DiazaCon™ (Avitrol Corp, Tulsa, OK, USA) and nicarbazin have already been developed at the National Wildlife Research Center (NWRC) as avian contraceptives. DiazaCon™ is a cholesterol mimic with nitrogen substitutions for the hydrocarbons at positions 20 and 25. It reduces cholesterol synthesis by inhibiting the conversion of desmosterol to cholesterol, thereby reducing production of reproductive steroid hormones. Nicarbazin is an anti-coccidial drug used routinely in the poultry industry. Through adverse effects on the vitelline membrane, nicarbazin prevents hatchability. At higher dose levels, nicarbazin also interferes with the deposition of egg yolk components, causing a reduction in egg production. Although both of these are promising contraceptive agents, more are needed for a wider variety of situations.
Past research at NWRC has focused on other cholesterol inhibitors, inhibitors of the P450 side chain cleavage enzyme, aromatase inhibitors, and melatonin. Future research will focus on natural products with contraceptive activity. These may include plant products containing high concentrations of phytosterols, phytoestrogens, saponins, and anti-gonadotropic compounds.
When choosing compounds to test as potential avian contraceptives, the ultimate goal of registration must be kept in mind. Adverse health effects, longevity in the environment, and secondary hazards must all be considered. Registration requirements should be kept in mind when designing efficacy studies.