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Sheep questions, Research continues into Bighorn sheep

by Wyoming Livestock Roundup

Laramie – Wyoming Game and Fish Department (WGFD) Wildlife Disease Specialist Hank Edwards continues to work toward increasing the available data on what has caused the tremendous decline in Bighorn sheep populations over the last two decades.

“These projects have been going on for a long time,” Edwards says. “We have a couple of herds of Bighorn Sheep that just aren’t doing well, and they haven’t done well for 20 years or more.”

“We are undertaking efforts to figure out why and to figure out what is really going on,” he continues.

Research goals

While domestic sheep can have some impact on the Bighorn sheep populations across the West by spreading a fatal strain of Pasteurella haemolytica, Edwards adds that several of the herds that see suffering populations have no exposure to domestic sheep.

In Wyoming, WGFD has studied seven different populations of Bighorn sheep, from the areas surrounding Jackson, Cody, Dubois, Sybille Canyon and in the Black Hills around Newcastle.

“We’ve been working on these projects for the last couple years, and a part of that is to try and map the presence of pathogens across the state to see which herds they are in and how those herds are performing,” Edwards explains.

He notes that the study will require at least one more year before data can be released and before he feels that they will have a handle on the presence of pathogens in Bighorn sheep across the state.

“We’ve also increased our sensitivity in the lab by improving lab techniques, so we are finding things now that we weren’t able to find two or three years ago,” he comments. 

Edwards marks the projects as WGFD’s largest Bighorn sheep research effort, but he also notes that they have captured some Bighorn sheep from the Cody area for further research at the Sybille Canyon.

Sybille research

Edwards says WGFD research will isolate sheep at the Sybille Canyon research facility.

“Each ewe is put into an individual pen, and we will allow her to lamb,” he explains. “Then, we see how long that lamb survives. If it doesn’t survive, we want to know which pathogen killed the lamb.”

In free-ranging Bighorn sheep, lamb groups socialize and play together, which can spread pathogens between animals. 

“If we have one ewe that is shedding harmful or deadly pathogens, she transmits them to her lamb,” Edwards continues. “We are trying to prevent mass deaths by separating the sheep to see which pathogens are responsible.” 

By comparing pathogens hosted on surviving lambs to those on deceased lambs, Edwards notes that the culprit pathogens can be identified.

“We want to know which pathogens the mother is carrying, if they are pathogenic or if there is another reason causing the death of lambs,” he says.

Lamb survival

Currently, in some herds across the state, lamb survival is nearly zero percent, which is problematic.

“We want to mix ‘dirty’ sheep, or those animals with very poor lamb survival, with those sheep carrying the same basic pathogens that do have very good survival rates,” says Edwards. “Can we mix those two populations together? What happens if we do? These are all questions that we want to answer.”

A multitude of possibilities exists, including loss of lambs, loss of adults or the possibility of shared resistance.

“It would be great if we can boost the survival rates by mixing populations,” Edwards says, “but that study won’t be complete for several years. We have a lot of work to do before we are ready to handle that many sheep.”

Mingling studies

Intermingling “dirty” sheep with clean populations can also help researchers to determine if those infected animals could be used to supplement the dwindling populations.

“We are asking if we can use some of our ‘dirty’ herds to augment those herds of sheep that aren’t doing well,” explains Edwards. “We know that if we bring in clean sheep and mix them with dirty sheep, they die. We are hoping, however, that is it possible to bolster some of those populations.”

“We don’t know if that is possible or not,” he adds.

Physical symptoms

At the same time they are identifying which sheep are shedding bacteria resulting in lamb death, Edwards notes that they are looking for physical symptoms in those animals.

“If we can identify those ewes that are shedding large amounts of bacteria so we can remove them from the herds, we can hope to build the overall health of the herd,” he says. “We will be looking for the signs and symptoms that we can see to identify those animals.”

Identifying symptoms – such as a cough or runny nose – in ewes may allow their removal and increase herd survival rates in the longer term.

Agriculture implications

With domestic sheep being implicated for Bighorn sheep deaths, Edwards says, “Domestic sheep can transfer Pasteurella haemolytica to Bighorn sheep, which is very pathogenic to the Bighorn sheep.”

However, he further explains that Bighorn sheep populations also live with a form of the P. haemolytica bacteria.

“Another part of our research is to find out why the strain from domestic sheep is so pathogenic and so more detrimental to Bighorn sheep herds,” Edwards adds.

At the end of the project, he notes that they hope to identify pathogens and identify those sheep shedding the pathogens to improve the survival rates of Bighorn sheep in the wild. 

“We are attempting to answer the question, what is going on?” he says. “This is a lot more complex than we thought. There are a multitude of factors that interact, and sorting them out isn’t easy.”

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

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