Bighorn sheep (Ovis canadensis) populations in North America have suffered great losses from pneumonia after coming in contact with domestic sheep and goats that graze on public lands. Now, a new study published in the Wildlife Society Bulletin suggests that small flocks on private land can also be a threat.
“In all of the West, the majority of bighorn sheep herds have had pneumonia outbreaks because of domestic sheep and goats. It affects almost every state in the western U.S. and their bighorn sheep, said Laura Heinse, a conservation partnership manager at Palouse Conservation District in Pullman, Wash., and one of the study authors. “And then after the herd contracts it, they can lose about 70 percent of the herd in the first year. The following few years, the lamb production is really low and they can lose the whole lamb crop.”
However, most management efforts in the past decade have focused on contact between wild and domesticated animals on public lands, so Heinse and her team wanted to know more about the impacts on bighorns from small flocks of sheep and goats on private lands. In 2014 and 2015, the researchers surveyed private farms near bighorn habitat in Washington state. They took samples of nasal mucus from a total of 137 sheep and goats from 24 flocks. Nearly 38 percent of these flocks tested positive for the bacterium, Mycoplasma ovipneumoniae.
Although the bacterium rarely produces disease in domestic animals, it has been linked to the development of pneumonia in bighorn sheep. Transmission occurs when the animals come in contact. After picking up the bacterium, the infected bighorns become susceptible to more pathogens that can cause fatal polymicrobial pneumonia. In the study, the researchers also found that domestic animals in 78 percent of the infected flocks had escaped their enclosures, which could put them in physical contact with bighorns in the area.
The researchers were also interested in how much the farm owners knew about the risk of pathogen spillover to bighorn sheep. Of 34 survey owners who responded to the survey, 32 percent had not heard of the risk, 15 percent were well informed and 53 percent knew only a little. All surveyed owners were willing to help prevent the spread of the disease in some of the ways the researchers suggested, especially if they were offered incentives.
“Certainly the best thing to do to prevent bighorn interaction is to not have any sheep or goats,” Heinse said, adding that owners are not required by law to keep their flocks away from bighorns.
However, most owners would not go that far. Most responded that they would not get rid of their flocks because they are useful for reducing the risk of wild fires and curbing growth of invasive vegetation. Further, many small farmers regard their goats and sheep as pets or prize animals.
More practical ways for keeping these animals away from bighorns include installing fences, signaling state biologists about sightings of bighorns near farms, and buying disease-free animals.
Outreach programs to educate farmers about the risk of disease transmission would be beneficial, Heinse says. However, she says that more effective ways of keeping the wild and domestic animals from coming in contact are also needed.
Margarita Yatsevich is a freelance writer.