Family Planning on the Range: The Battle Over Bison Contraceptives

Could contraceptives offer protection for the nation's last continuously wild herd of American bison?


At feeding time, residents of the Brogan Bison Facility cluster around a hay bale, blinking at flecks of alfalfa dust that swirl in the air and settle in their shaggy coats. The herd, chewing and lowing, mills in a holding pasture near Corwin Springs, Montana, surrounded by sweeping mountain views and a seven-strand wire fence. Blue-painted squeeze chutes are settled in the dirt nearby, bordered by a swath of prairie grass that stretches for a few miles until it meets the northern border of Yellowstone National Park. This, under a graying sky beginning to spit the first snowflakes of another long winter, is the unlikely center of a contentious debate over birth control.

The bison, gathered after drifting out of Yellowstone earlier this year, are potential subjects of a USDA study of GonaCon, a contraceptive vaccine for wildlife. Originally developed by the USDA as a non-lethal form of pest control, GonaCon works by lowering the concentration of sex hormones in the bloodstream to weaken fertility and the urge to mate. The contraceptive was recently approved in Maryland and New Jersey for curbing the population of wild deer. Now researchers are hoping to use GonaCon to stop the spread of brucellosis, an infectious bacterial disease that causes pregnant ungulates to abort their calves.

The Greater Yellowstone Area is the last known reservoir of Brucella abortus bacteria, believed to have been introduced to the park's bison by domestic cattle at the beginning of the 20th century. Roughly half the bison population in Yellowstone tests positive for exposure to the disease, which is primarily transmitted by contaminated birthing materials deposited on grazing grounds. Brucellosis also poses a threat to neighboring cattle herds when infected animals wander over the park's invisible boundaries. Researchers from the USDA's Animal and Plant Health Inspection Service (APHIS) are interested in whether temporary sterilization with GonaCon can prevent the shedding of bacteria-riddled afterbirth and help block disease transmission.

The USDA has spent close to two billion dollars over nearly eight decades trying to stamp out the disease, which carries hulking environmental and financial consequences. Bison who leave the park to seek food at lower elevations are routinely rounded up and quarantined, and those found to have the disease are slaughtered. When brucellosis crops up on cattle ranches, herds must be quarantined and infected members butchered. Additionally, the bacteria can pass to humans through unpasteurized milk. Jack Rhyan, a veterinarian medical officer and wildlife pathologist with APHIS, and the study's principal investigator, said that the focus on brucellosis is driven in part by its implications for public safety. "Animal health is directly related to human health," he said.

But while the GonaCon study is still in the nascent stages, some conservationists are already voicing concerns. Stephany Seay, media coordinator of Buffalo Field Campaign, a group that advocates for protection of the Yellowstone herd, views the USDA study as an experiment in population control. "Brucellosis is being used as a tool to manipulate the movement of wild bison," she told me. According to Seay, GonaCon is a means of catering to ranchers who don't want to compete with bison for grassland. "This is a centuries-old range war," she continued.

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Sarah Yager is a senior associate editor at The Atlantic.

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