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Birth control shot shows potential

Colorado State University researchers are working to perfect two short-term birth control methods that may eventually be injected by dart into wild animals such as elk, providing options for managing wildlife overpopulation in protected areas across the country.

Wildlife overpopulation plagues state and national parks across the nation and world, with overcrowding from bison, deer, elk, wild horses and other species causing damage to native habitat and impacting the diversity and abundance of other species that share the same space.

“Hunting and culling have traditionally been used to regulate animal numbers in the wild, but other approaches that meet public approval are needed in parks and urban areas where these methods are not feasible,” said Dr. Terry Nett, a researcher at Colorado State University’s Animal Reproduction and Biotechnology Laboratory and the Department of Biomedical Sciences.

“Controlling the fertility of female mammals may eventually prove to be an effective alternative for population control, but more testing is needed before this goal can be realized.”

One approach has been shown to be 100 percent effective as a contraception in mule deer and elk for one breeding season while the other method may provide contraception for two to three years and is 75 percent to 90 percent effective.

Recent research by the university’s College of Veterinary Medicine and Biomedical Sciences on female elk showed that a drug called leuprolide, which is used to treat endometriosis and fibroid tumors in the uterus, and a vaccine called GonaCon show promise as wildlife contraceptives.

Each influence a hormone called gonadotropin-releasing hormone, or GnRH, and suppress ovulation in female mammals by altering normal function of the pituitary gland. A slow-release formulation of leuprolide prevents the pituitary gland from functioning for 6 months to a year, preventing pregnancy for one breeding season.

The GnRH vaccine, GonaCon, causes an immune response that neutralizes the animal’s own GnRH and prevents the pituitary gland from stimulating the ovaries for up to 3 years in some species.

Both can be administered by dart, eventually making the technology more useful to wildlife managers.

Research shows that neither method significantly impacts social behavior of the herd during the breeding season. However, GonaCon may increase individual male and female interactions during the breeding season.

Ongoing studies at Colorado State will determine how long the approaches impact fertility. Studies also will look for long-term impacts on reproductive system development in calves that are the offspring of treated females. The growth rates and survival rates in the offspring of previously treated elk do not appear to be affected in preliminary studies.

While the GnRH vaccine does not impact current pregnancy in animals, leuprolide must be administered when the animal is not pregnant.

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