ODFW steps up disease monitoring in California bighorn sheep

SALEM, Ore. — ODFW is increasing disease monitoring in California bighorn sheep throughout Oregon this year as part of ongoing research with Oregon State University and the Western Association of Fish and Wildlife Agencies.

ODFW traditionally relocates sheep each year as part of a years-long effort to restore this rare species to its historic range in Oregon. But these relocation efforts are on hold this year while wildlife managers learn more about Mycoplasma ovipneumonia (M. Ovi, the bacteria primarily responsible for infectious pneumonia in bighorn sheep).

In the last few weeks, ODFW wildlife biologists and veterinarians have sampled 54 bighorn sheep in southeastern Oregon. Paired with previous year’s capture efforts, this brings the total of disease sampled and collared California Bighorn Sheep to over 120.

Concerns about how M. Ovi is impacting Oregon’s wild sheep populations have grown since a die-off of the Lower Owyhee bighorn sheep herd in 2015-16. Also that year, the Nevada Dept of Wildlife made the difficult decision to eliminate an entire herd of sick bighorn sheep just south of Oregon’s border to stop the spread of M. ovi to neighboring populations.

Respiratory disease has killed numerous wild sheep in Oregon and other Western states over the past few decades and is considered the largest risk to wild sheep populations. Once a herd is infected, an all-age die off can occur and the disease remains chronic in the population.

Disease treatment in free-ranging populations of sheep is not practical, so wildlife managers strive to keep wild and domestic sheep and goats separate to avoid transmission of the disease. Working collaboratively through WAFWA and its Wild Sheep Working Group, Western state wildlife agencies are also evaluating how herds respond to the disease, the risk of translocating animals between herds infected with identical strains of the disease and how to increase survival rates of wild sheep.

Disease monitoring involves taking a variety of samples from each sheep after they were captured by helicopter by Quicksilver Air. These include blood, nasal and tonsillar swabs, and fecal samples looking at a variety of pathogens affecting bighorn sheep. These tests can help answer questions as to whether bighorn sheep have active infections, have been exposed in the past, and how well an individual may be able to fight off infections.

“When we get our hands on an animal we take full advantage and try to maximize what we learn from it,” says Julia Burco, ODFW wildlife veterinarian. “These samples will give us a much better understanding of the extent of the bacteria in Oregon’s sheep, if infections are active, and if wild sheep can fight it off and survive.” Each sheep was also fitted with a GPS collar to track its movements.

The 102 samples taken are now being tested by Oregon State University Veterinary Diagnostic Laboratory and Washington Animal Disease Diagnostic Laboratory with results expected later this month. Samples from previous years showed there are different strains of M. ovi affecting Oregon’s sheep herds. Testing will also help determine if the strain that eliminated the Nevada herd spread to Oregon’s sheep.

Successful bighorn sheep hunters have also provided samples and helped in tracking pneumonia in Oregon bighorn sheep herds. Of 43 hunter-harvested sheep tested in 2015, three sheep from the Owyhee herd were actively shedding the bacteria. Results from the 2016 hunting season are not yet available.

Oregon is home to about 3,700 California bighorn sheep in 32 different herds in central and southeast Oregon. There are also about 800 Rocky Mountain bighorn sheep in northeast Oregon.