Anyone owning or thinking of purchasing domestic sheep or goats and are living in or close to wild bighorn sheep native range should be aware of potential lethal consequences for the wild sheep.
On March 8 biologist Chris Procter presented a research paper to a number of interested people at the Scout Island Nature Centre. Chris grew up in Williams Lake and now works out of Kamloops and along with coauthor Jeremy Ayotte wrote a research paper entitled Fraser River Bighorn Sheep Disease Mitigation Program 2022 Progress Report.
The following are some of the highlights from the report. I have left out some of the references and encourage readers to download the progress reports for more details including tables and maps.
“Bighorn sheep (Ovis canadensis) are an iconic wildlife species in British Columbia and respiratory disease is currently affecting several bighorn sheep herds in the province, including the California big horn sheep (Ovis canadensis californiana) along B.C.’s Fraser River, which is an important population for First Nations, licensed hunters, and the public.”
The report goes on to note that current science suggests bacteria (M.ovi) is the single most important pathogen implicated in pneumonia-related die-offs of wild sheep and is considered the largest threat to wild sheep in North America. An important source of infection is domestic sheep and goats, which are better adapted to the disease and can live with it with few ill effects.
Procter and Ayotte report that once infection occurs, the disease is complex and can persist in populations for many years with no signs of recovery.
Following initial exposure, some wild sheep die, at times up to 100 per cent of herds may die, some sheep develop strain-specific immunity, and some sheep live with the disease and become carriers of the bacteria, shedding the bacteria through their nasal passages.
The bacteria are passed between individuals in close contact and the annual chain of transmission is generally from a female carrier to their young lamb which then pass along the bacteria to other lambs in the nursery groups during the summer months.
Research has shown the bacteria causes summer lamb pneumonia, high levels of lamb mortality within their first couple months of life and the result is persistently low lamb recruitment, which prevents long-term recovery of the sheep population, noted the authors.
The disease persists until all individuals that carry the bacteria naturally die out, which can take a long time, and new carriers may enter the population over time as surviving lambs can become future carriers.
Previous research indicates that Fraser River bighorns have likely been exposed to M.ovi in the past.
If contact with domestics occurred in the distant past, it appears that wild sheep may have recovered given that the Fraser River populations observed in the early to mid 1990s were the highest ever recorded.
At that time, there were more than 2,400 sheep along the Fraser River north of Lillooet. In the mid to late 1990s, Fraser River bighorn sheep suffered a pneumonia-related die-off and declined in all areas.
Procter and Ayotte noted currently there are approximately 800 sheep in the same area, approximately a 70 per cent decline.
Initially, the late-1990s declines were attributed to lungworm and other pneumonia-causing bacteria, however, little was known about M.ovi at the time and the technology did not exist to test for the presence of it.
“We now understand that M.ovi is a primary causal agent of pneumonia in bighorn sheep and we suspect that M.ovi was implicated in those initial declines without our knowledge.
“We further assume the lack of recovery, and continued declines in some bands of sheep, is due to persistent effects of M.ovi infection on lamb survival since that time. In 2011, M.ovi was officially detected for the first time in sick lambs from the Pavilion and Big Bar Creek area.
“The implementation of the Fraser River Disease Mitigation Program consists of two key phases. Phase 1, surveillance sampling to document the distribution of M.ovi along the Fraser River and Phase 2, test and remove treatments and treatment effectiveness monitoring.”
In a future article I will present more information on the details of the sampling and treatment program.
Jim Hilton is a retired forester who spent his career working in the Cariboo Chilcotin.