Development of Injectable and Oral Contraceptive Technologies and Their Assessment for Wildlife Population and Disease Management
PROJECT GOALS: To develop injectable and oral contraceptives to manage overabundant wildlife populations and reduce the spread of zoonotic diseases.
Project Accomplishments 2010
GonaCon™ Efficacy in Elk— Overabundant populations of elk (Cervus elaphus) are a significant concern in some areas of the western United States because of the potential ecologic damage they can cause and their risk of spreading brucellosis ( Brucella abortus) to domestic livestock. Brucellosis is transmitted among elk through direct contact with aborted fetuses, placentas and associated fluids, or postpartum discharge of infected animals. Because the transmission of brucellosis is dependent on pregnancy, using contraception in cows (female elk) could help both to manage the disease and to manage elk populations.
NWRC scientists, in collaboration with other APHIS researchers and the Wyoming Game and Fish Department, evaluated the contraceptive efficacy of a gonadotropin-releasing hormone vaccine (GonaCon™) in female elk. In 2004, cows were given a single immunization of either 1,000 milligrams or 2,000 milligrams of GonaCon and were then compared with a group of control elk. In 2004, 2005, and 2006, cows were grouped with bulls for the breeding season. Blood samples were taken each spring for pregnancy testing, progesterone assays, and antibody titers. For cows given 1,000 milligrams of GonaCon, 86, 90, and 100 percent were infertile during 2005, 2006, and 2007, respectively. For cows given 2,000 milligrams of GonaCon, 90, 100, and 100% were infertile. Rates of infertility for control cows were 23, 28, and 0% for the same periods.
These results indicate that either dose of GonaCon prevented the pregnancy of elk cows for at least three years. The researchers conclude that GonaCon has potential as part of an integrated strategy to control brucellosis and manage elk populations.
Diazacon Use in Rose-Ringed Parakeets—Rose-ringed parakeets (Psittacula krameri), also known as ring-necked parakeets, are native to central Africa and Asia, but through accidental and deliberate release, populations are now established in Europe, Japan, and the United States. As an invasive, non-native species, the rose-ringed parakeet has raised conservation concerns, because its early breeding season and preference for established nest cavities places it in potential conflict with native cavity-nesting birds. Potential economic impacts on agriculture, conservation concerns, and mixed public opinion regarding the species have highlighted the need to develop new management options.
The chemical 20,25-diazacholesterol dihydrochloride (diazacon) has previously been used to reduce reproductive output in avian species through reduction of blood cholesterol and cholesterol-dependent reproductive hormones. In a recent study, NWRC and researchers at the United Kingdom's Food and Environment Research Agency orally dosed captive rose-ringed parakeets with a solution of either 9 milligrams/kilograms (mg/kg) or 18 mg/kg of diazacon for up to 10 days. Researchers found that a dose of 18 mg/kg for 10 days temporarily reduced blood cholesterol levels with no adverse side effects. Further evaluation showed the 18 mg/kg-dose level reduced fertility in rose-ringed parakeets in a captive breeding population. Egg fertility rates were reduced by 54.2% for the first clutch and 66.5% for the second clutch, compared to control birds.
Based on these results, researchers conclude that diazacon has potential for fertility control in rose-ringed parakeets if a suitable formulation and delivery system is developed for free-living populations.
NWRC's economist modeled the cost effectiveness of using OvoControl-G versus egg addling, oiling, or other nest-destruction techniques to manage nuisance Canada geese at two locations in Oregon. Assuming that the biological effects of egg oiling, addling, and destroying nests are similar to those of OvoControl G, researchers used a cost-effectiveness analysis (CEA) to evaluate the costs associated with the different methods and determine which method minimizes those costs. The model also evaluated the effects of the presence of nontargets, alternative foods, and public support on cost efficacy. Results showed that at low goose densities (less than 35 pairs of geese), fixed labor was a significant portion of costs. As goose densities increase, OvoControl-G becomes more cost effective than other methods, such as egg oiling or addling.
The analysis provides useful information for wildlife managers, as they can use this model to determine whether OvoControl-G will provide a successful and cost-effective tool for controlling populations of Canada geese in specific management areas.