Arizona’s Bighorn Sheep Population Under Threat Of Disease

Due to multiple incidents of domestic sheep escaping their enclosures in southwestern Arizona, Arizona’s wild bighorn sheep population is in peril, according to Arizona Game and Fish.

Arizona Game and Fish (AZGFD) officials advise that starting as far back as late September, an estimated 300 domestic sheep escaped temporary grazing areas on private land. Some have been rounded up but an unknown number with contagious diseases known to kill bighorns are unaccounted for. The escaped domestic sheep dispersed into bighorn sheep habitat in Yuma County.

Because these domestic sheep were observed mixing with bighorn sheep that live in the area, AZGFD has taken necessary steps to stop the transmission of disease. Domestic sheep have long been known to carry diseases for which bighorn sheep have limited defenses, and direct contact is not necessary to transmit disease. According to Mike Sumner, AZGFD regional supervisor, a small number of bighorns were euthanized to keep disease from spreading to other animals in the area.

“This is something no wildlife biologist wants to undertake, but to protect the 700-800 bighorn sheep that live in these mountains, we had to euthanize some individuals that had come in contact with domestic sheep,” said Sumner. “We value these individual animals, but must manage for the health of the whole bighorn population.”

On October 19, AZGFD personnel verified the presence of domestic sheep in bighorn habitat, and their owner gave the Department permission to remove them. Some of the domestics were found to be infected with contagious ecthyma, a painful disease which can prevent lambs from nursing and lead to mortality. The risk for disease transmission was considered high because of the length of time the domestic sheep were loose. Some domestic sheep as well as three bighorn sheep had to be euthanized.

In 2015, almost 40 percent of two bighorn herds in Montana north of Yellowstone National Park died after exposure to domestic ovine pneumonia. In the early to mid-1990s, domestic sheep and feral goats infected bighorns near Hells Canyon, Idaho, causing a catastrophic die off lasting almost a decade and killing 70 percent of the bighorn sheep populations spanning large areas of Idaho, Washington and Oregon.

AZGFD followed the guidelines of the Western Association of Fish and Wildlife Agencies, which recommend euthanizing bighorns that have likely associated or had direct contact with domestic sheep or goats to reduce the spread of disease. Similar actions were taken in Utah (2010), Washington (2013) and Nevada (2016) to protect the larger bighorn populations.

According to AZGFD Veterinarian Anne Justice-Allen, quarantining bighorns for observation and treatment was not an option because it would take 4 to 6 weeks of repeated sample collection and testing to learn if these bighorn sheep were indeed infected.

“Holding wild bighorn sheep for that period would be stressful and likely would cause several animals to die,” said Justice-Allen. “In addition, the Department has no suitable holding facility. Relocating them to a zoo was not possible because of the risk of disease transmission.”

The escaped domestic sheep caused other problems for the Arizona Department of Agriculture, law enforcement and health officials. More than 50 domestic sheep were found dead in a canal in the Wellton-Mohawk Irrigation and Drainage District.

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