Nonsurgical sterilization research gives birth to new veterinary tools

NATIONAL REPORT — Researchers are making progress in the push to create new methods for non-surgical sterilization.

University of Florida (UF) veterinary researchers, in collaboration with the U.S. Department of Agriculture (USDA), recently discovered that a contraceptive developed by USDA's Animal and Plant Health Inspection Service National Wildlife Research Center can be used to control fertility in adult female cats for several years.

"We're hoping this research will lead to a non-lethal method of control for feral cat populations that is less expensive, labor-intensive and invasive than current methods, such as surgical sterilization," says Dr. Julie Levy, DVM, PhD, the lead researcher on the study and director of the Maddie's Shelter Medicine Program at the University of Florida.

The five-year study was funded by the Morris Animal Foundation, and its findings were recently published in the scientific journal Theriogenology.

The aim of the study, according to UF's Sarah Carey, is to aid in the registration and use of the vaccine, called GonaCon, to manage feral cat populations.

GonaCon is currently registered with the U.S. Environmental Protection Agency for use on female white-tailed deer, but has been found to be successful in other animals, including feral horses, bison, elk, prairie dogs and squirrels, Carey says. The single-shot, multi-year vaccine stimulates the production of antibodies that bind to GnRH, the hormone that signals the production of hormones like estrogen, progesterone and testosterone. The vaccine works to keep animals in a non-reproductive state as long as sufficient levels of antibodies are present.

In the new study, 15 adult female cats were given a single dose of the vaccine while five cats received a placebo. The females were then given access to a breeding male cat. All five placebo females became pregnant within seven to 28 days, while the females that received the vaccine remained infertile from five months to more than five years.

"A total of 93 percent of the cats treated with GonaCon remained infertile for the first year," Levy says. "In subsequent years, we saw a steady and expected decline in infertility as antibodies to the vaccine decreased. However, numbers were still quite high, with 73 percent of the cats remaining infertile during the second year, 53 percent in year three, 40 percent in year four, and 27 percent in year five when we ended the study."

Although permanent sterilization is ideal, Carey says even a multi-year solution could be successful in reducing populations of free-roaming cats, which tend to have a relatively short lifespan.

And there are other non-surgical approaches in development. An Arizona company called Senestech also developed a new drug, which it hopes to introduce into Arizona animal shelters. Chemspay was developed "accidentally" by biologist Dr. Loretta Mayer, who was looking for a way to artificially induce menopause in mice so they could be used in a study on human disease. The result was the development of a drug called ContraPest, which Mayer tested in 2007 on rat populations in Indonesia. From 2004 to 2007, she tested a version developed for female dogs called Chemspay. The trials indicated that Chemspay, which can be administered orally or by injection, significantly reduced the number of eggs in the tested dogs, making them sterile. The company reports the drug is still six to nine years from gaining FDA approval.

Research is also underway on nonsurgical sterilization methods at multiple institutions as part of the Michelson Grant in Reproductive Biology program by the non-profit organization Found Animals. The foundation accepts proposals for up to $250,000 per year for up to three years of funding, and received 160 letters of intent since October 2008. More than 50 researchers have been invited to submit full grant applications and, to date, 15 grant proposals totaling $6 million have been approved.