“Pneumonia” and “bighorns” have become dependable stalking horses for groups wanting to shut down sheep grazing on federal land. In a recent effort, anti-grazing groups made dubious claims about the risk of contact between domestic sheep and bighorn sheep their own arguments don’t seem to support.
The Western Watersheds Project, together with WildEarth Guardians, launched a lawsuit and sought a restraining order against the U.S. Forest Service (USFS). Their goal is to prevent sheep grazing in the Caribou-Targhee National Forest in Idaho that could begin Nov. 6. The groups equate any contact with sheep to a deadly threat of pneumonia to nearby bighorns.
The groups claim USFS violated the National Environmental Policy Act (NEPA) by authorizing domestic sheep grazing on the Snakey Canyon and Kelly Canyon allotments before an ongoing NEPA assessment was completed. They ask the District Court of Idaho to declare the authorization unlawful and to block grazing on the allotments for 2017-2018.
The allotments are grazed by U.S. Sheep Experiment Station (USSES) sheep owned by the University of Idaho. The allotments also overlap the core home range of the South Beaverhead population of bighorns. In 2016, the population was estimated at 36 animals.
“Bighorn sheep experts and wildlife managers uniformly agree that domestic sheep can transmit pathogens to bighorn sheep, which usually results in pneumonic disease die-offs in bighorn herds,” reads part of the restraining order request’s “Statement of Facts” section.
“The only way to prevent disease transmission is to keep the domestic sheep and bighorn sheep physically separated,” Sarah McMillan, conservation director of WildEarth Guardians, asserted in the group’s announcement of the suit.
“The agencies know this. Nevertheless, the Forest Service is planning to keep domestic sheep within the range of the South Beaverhead population for months, even though this bighorn herd is already at risk.”
Inconsistencies
Despite the dire tone taken by the plaintiff groups, the complaint and restraining order request both present information that does not seem to support their claims. In its “Statement of Facts” section for instance, the complaint outlines that sheep have grazed the area for some time, that they can and have interacted with bighorns during this time, and that the bighorn population seems to have grown.
The complaint notes the allotments have been grazed by USSES sheep “for years” and at a lower stocking rate and for less time than authorized. Elsewhere, the 2016 population of 36 head is the highest population listed. Additionally:
“The Snakey Canyon and Kelly Canyon allotments have bighorn sheep habitat that is open and easily accessible by South Beaverhead bighorns. … The telemetry data [from radio-collared animals in the population] shows bighorns making numerous movements and using a large portion of the habitat during fall and winter.
“The open habitat also makes it easy for domestic sheep from the allotments to go upslope into the areas consistently used by the bighorn population.”
WLJ reached out to USSES regarding the lawsuit, but representatives could not comment due to the ongoing litigation. The American Sheep Industry (ASI) Association responded to WLJ, with Senior Policy and Information Director Chase Adams saying:
“This charge brought by Western Watersheds is a clear example of what happens when you try to litigate science. Their pleadings are false on their face, disease is not transmitted, and domestic sheep are not ‘immune’ to the pathogens that lead to die-offs,” he said, referring to a claim made in the suit.
“Yet Western Watersheds and other radical environmental groups continue to rely on flawed science to harass agriculture on all fronts. The American Sheep Industry will continue to work to ensure grazing decisions on public lands are based on sound science and protect the critical research being done by the U.S. Sheep Experiment Station.”
Pneumonia
Very basically, pneumonia is an infection of the lungs. The infection can be caused by bacterial or viral agents, or even foreign material such as dust. Infections result in inflammation, which in turn results in fluid building up in the alveoli; the tiny air sacs that make up the lungs.
In bighorns, the pathogen of interest is the bacterium Mycoplasma ovipneumoniae, sometimes called “movi.” It is ubiquitous in North American habitats. In an in-depth study by USDA’s Animal and Plant Health Inspection Service (APHIS) done on domestic flocks in 2011, movi was found in every sampled range flock. Managing movi is an ongoing challenge for domestic sheep producers.
Movi is not the only pathogen that can cause pneumonia in bighorns. Additionally, a causal link between movi and the fatal pneumonia in bighorns is not certain despite the plaintiff groups’ claims.
For example, a controlled experiment in 2009 by Washington State University researchers was not able to reproduce fatal pneumonia in bighorns simply through exposure to movi. It was only in combination with another pneumonia-causing bacterium, Mannheimia haemolytica, that fatal pneumonia was observed. This suggested to the researchers movi “alone may not cause fatal pneumonia in [bighorns], but can predispose them to fatal pneumonia due to M. haemolytica infection.”
Maggie Highland, DVM, a veterinary anatomic pathologist and infectious disease researcher with the USDA’s Animal Research Service, has stressed to both WLJ and ASI in the past that the presence of movi does not translate to fatal pneumonia. This makes the conflation of contact with sheep to deadly pneumonia in bighorns all the more tenuous.
“Diseases are not ‘transmitted;’ infectious agents are transmitted,” she told ASI during last year’s conference. She added that disease formation—in this case, pneumonia—is dependent on many things, including overall health and environmental stressors.
Shortly after the conference, Highland told WLJ that, “The oddity of this all is the fact that [movi] is an endemic agent in North American small ruminants, yet there is a desire to make wild small ruminants completely free and naпve of exposure to this bacterium.”
Don Knowles, DVM, a professor of veterinary microbiology and pathology at Washington State University, pointed out in his own presentation at the past ASI conference that, “Endemic infectious diseases are controlled by acquisition of immunity through exposure/recovery and/or vaccination.”
The current practice regarding bighorns that have come in contact with domestic sheep, and supposedly contracted movi as a result, is to “capture and remove” those individuals before they return to their home herds. This generally means killing them.
“It has become policy in some cases to kill (shoot) survivors of herds that experience outbreaks of pneumonia—I know of a case in which just over 200 surviving animals were killed— then bring in new bighorns to repopulate the area, without really understanding all of the factors that caused the first outbreak,” Highland mused to WLJ in the past.
She, Knowles, and many others have suggested human-caused stresses may have a hand in risking bighorns.
“The focus on reservoir sources of infectious diseases is only one component of endemic infectious disease control, it is paramount to look broadly at all possible influences on bighorn herd health, including management practices,” Knowles told ASI. — Kerry Halladay, WLJ editor
