Overabundant populations of elk (Cervus elaphus) are a significant concern in some areas of the western United States because of potential ecologic damage and spread of brucellosis to domestic livestock. Brucella abortus is transmitted among elk through direct contact with aborted fetuses, placentas and associated fluids, or postpartum discharge of infected animals. Because transmission of brucellosis is dependent on pregnancy, contraception of cows could be used for both disease and population management. The objective of this study was to evaluate the contraceptive efficacy of a gonadotropin-releasing hormone vaccine (GonaConTM) in female elk. In September 2004, cows were given a single immunization of either 1,000 μg (n=12) or 2,000 μg (n=10) of GonaConTM and compared with a group of adjuvant-treated controls (n=15). In November 2004, 2005, and 2006, cows were grouped with bulls for the breeding season. Blood samples were taken in February 2005 and March 2006 and 2007 for pregnancy testing, progesterone assays, and antibody titers. For cows given 1,000 μg GonaConTM the percentages that were infertile for 2005, 2006, and 2007 were 86%, 90%, and 100%, respectively, compared with 90%, 100%, and 100% for cows given 2,000 μg GonaConTM. Rates of infertility for control cows were 23%, 28%, and 0% (P<0.0001). The results indicated that either dose of GonaConTM prevented pregnancy of elk cows for at least 3 yr. We concluded that GonaConTM use for population management of elk warrants consideration as part of a strategy to control brucellosis.
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Vol. 45 • No. 1