Skip to Content

The Weekly News Source for Wyoming's Ranchers, Farmers and AgriBusiness Community

Experimental vaccine in development for Bighorn sheep

by Wyoming Livestock Roundup

A research team at Washington State University (WSU) has developed an experimental vaccine for Bighorn Sheep that allows them to fight the toxin-producing bacteria implicated in large die-offs of the wild sheep.

Subramaniam Srikumaran, a WSU Professor in Veterinary Microbiology and Pathology, explains, “We find that most of the organisms carried by the domestic sheep produce a toxin, and most of the organisms carried by the Bighorn Sheep do not. That is why, when the Bighorn Sheep get these organisms in their system, they die quickly.”

This bacteria resides in the nose, mouth and throat of domestic sheep and is shed when sheep cough or sneeze. The bacteria reside in the droplets expelled until they are picked up when Bighorn Sheep consume forage or breathe in the organisms. Additionally, the bacteria can be transferred through nose-to-nose contact.

When Bighorn Sheep pick up the toxin-producing bacteria from domestic animals, the toxin kills white blood cells, compromising their immune system. As a result, damage to the lungs develops and pneumonia sets in, ultimately killing the Bighorn Sheep.

“It is logical to focus on the transmission of these organisms and making the Bighorn Sheep resistant by vaccinating,” continues Srikumaran. “We developed an experimental vaccine and immunized four Bighorn Sheep.”    

The experimental vaccine utilizes the antigens of toxin-producing bacteria in in a modified form to avoid causing disease in the Bighorn sheep.

“We modify them in a way that doesn’t cause the disease, but structurally, it is the same, so the immune system of the body can respond,” explains Srikumaran.

Some of the cells of the immune system, known as memory cells, remain in the blood and circulate through the body, so when the bacteria is encountered again, the body can respond more rapidly and in a more pronounced manner, according to Srikumaran.

After vaccinating the Bighorn Sheep multiple times to increase antibody numbers, Srikumaran says they introduced a challenge test by putting the microorganism in the nostrils of the Bighorn Sheep. Four Bighorn sheep were vaccinated while four were unimmunized, serving as a control.

“All four of the unimmunized animals died, and all four vaccinated animals are still alive,” says Srikumaran, noting that this indicates initial success with the vaccine.

While there has been success with this vaccine, Srikumaran admits there is further work to be done.

“We used the vaccine four times,” says Srikumaran. “In wild animals, that isn’t practical. Even one injection is not really practical in Bighorn Sheep.”

“In the next three to five years, our focus is to come up with a vaccine that can be delivered intra-nasally or orally,” continues Srikumaran.

Srikumaran explains that Bighorn Sheep are fed pelleted feed in the winter when little food is available in the high mountains. The sheep would take in the vaccine while eating. However, developing an oral vaccine is both difficult and time-consuming.

In addition to the vaccine, Srikumaran’s team is working on a product to reduce the transmission of toxin-producing bacteria from domestic sheep.

“We found another bacterium that doesn’t produce a toxin,” says Srikumaran. “In the laboratory, we have shown that this bacteria can grow and eliminate the disease-causing bacteria. We plan to test in the animal in the next two to three years.”

This strategy would require domestic sheep producers to spray the helpful bacteria into the nose of sheep to reduce the number of toxin-producing bacteria and limit transmission.

“We don’t know whether it completely eliminates the disease causing organisms from the throat of the domestic sheep, but even if it significantly reduces the numbers in the throat of the domestic sheep, it is a big step,” explains Srikumaran.

Srikumaran praises the efforts of Wyoming in his research, saying, “The state of Wyoming has contributed more funds than any other state towards the research.”

Following the Bighorn Sheep meeting held in Denver, Colo. on June 13-14, three working groups discussed the possible options in resolving conflict of domestic sheep and bighorn sheep intermingling.

According to the American Sheep Industry Association (ASI), more than 80 participants were involved, including industry representatives, state and federal agency representatives, wild sheep advocates and sheep producers.

Among the results of the meeting, a number of recommendations were made, including support of research for vaccine treatments, consolidation of best management practices (BMPs), evaluation of BMPs and implementation of collaborative working groups.

Wyoming State Veterinarian and American Sheep Industry Animal Health Committee Chair Jim Logan has chaired a task force relating to Bighorn Sheep for a number of years, saying they have worked closely with the Game and Fish and Bighorn Sheep advocacy groups and are establishing relationships with the BLM and Forest Service.

“We developed best management action plans for both the wildlife and domestic sheep side of things,” says Logan. “We are hoping that we will be able to get concurrence on some new research and some funding.”

“A lot of research from the past wasn’t valid,” adds Logan. “Some newer research points that out, so there is a huge need for peer-reviewed and collaborative research so we get acceptable results that can be dealt with appropriately.”

He also pointed out that the research available may incorrectly implicate domestic sheep in all die-offs of the wild animals.

“The sheep industry readily agrees that in some situations, die-offs do occur in association with domestic sheep, but there are documented situations where die-offs do occur with no correlation to sheep,” explains Logan.

In Wyoming, Logan has been working on a task force appointed by Governor Jim Geringer in the mid-1990’s. The Bighorn/Domestic Sheep Working Group includes the state veterinarian, director of the Department of Agriculture, director of the Game and Fish, sheep industry representatives and Bighorn Sheep Advocacy groups.

Logan says, “At this point, we have gained a lot of ground in Wyoming.”

Saige Albert is assistant editor of the Wyoming Livestock Roundup and can be reached at

Back to top