Wyoming Bighorn Sheep Nutrition and Disease Project

Pneumonia outbreaks in bighorn sheep have become a conservation and management issue for wild sheep herds across North America. However, not all pneumonia outbreaks effect sheep populations the same and not all populations carrying pneumonia related pathogens have outbreaks. We aim to identify how disease and nutrition interact to effect population dynamics by researching bighorn sheep in the Gros Ventre, Wind River, and Absaroka ranges.

Our Hypothesis:

We suspect that the susceptibility of a bighorn sheep population to a pneumonia outbreak may be dependent on the nutritional quality of their landscape. For example, animals that live in habitats of lesser quality may be in poorer nutritional condition, and thus, less tolerant of pneumonia-causing pathogens. Conversely, animals in high-quality habitats may be in better nutritional condition and more resilient to pneumonia outbreaks.

What's the issue?

Pneumonia-causing pathogens are present in most bighorn sheep populations in Wyoming, but some populations are more resilient to outbreaks, when compared to others. This may be, in part, because individuals could carry pathogens related to pneumonia without being affected, while another with the same pathogens could have symptomatic pneumonia. Animals with access to high quality forage tend to be in better nutritional condition and may be better buffered from the effects of pneumonia-causing pathogens, when compared to animals with limited access to high quality forage. For example, Wind River sheep appear nutritionally limited on their summer range and are not tolerating pathogens as well as Gros Ventre sheep with more robust summer range. Nevertheless, the environmental factors that influence an animal’s susceptibility to contracting pneumonia are largely unknown.

How're we tackling it?

To understand the influence of animal nutrition in disease prevalence of pneumonia among bighorn sheep populations in northern Wyoming, we will recapture the same adult sheep each spring and autumn to track changes in nutritional condition, immunity, and pathogen prevalence of individual animals over time.

Nutritional condition: We will evaluate nutritional condition using ultrasonography to measure fat throughout the year.

Immunity: We will evaluate immune function measurements from blood samples from individuals.

Pathogens: We will detect presence of pathogens from tonsil and nasal swabs collected during captures.

Habitat quality: We will compare sheep diets and habitat quality (e.g., plant diversity, abundance, and nutritional quality) between the Wind River and Gros Ventre ranges and connect this information with the nutritional and medical history of individual ewes.

What are our findings?

Nutritional condition:

As expected, animals are in relatively good nutritional condition following summer and in poor condition following winter. Further, in most years, Gros Ventre (i.e., Jackson) sheep are in better condition than Wind River sheep (i.e., Dubois).

Nutritional condition (i.e., fat levels) of bighorn sheep of the Wind River (i.e., Dubois), Gros Ventre (i.e., Jackson), and Absoroka (i.e., Cody) ranges.


Bacterial pathogens found in our sheep include (proportion of animals testing positive):

Mycoplasma ovipneumoniae (AKA M.Ovi) *thought to be the primary pneumonia-causing pathogen.

Pasturella miltocida (AKA: Pasturella)

Mannhheimia spp.(including Mannheimia haemolytica)

Biberstenia trehalosi

What's the issue?

The life-history and decisions a mother makes often play important roles in her ability to successfully rear young. For example, bighorn sheep use fat stores to finance the cost of raising offspring. The additional energetic resources needed to finance immune function may lead to less energy available for raising a lamb. Furthermore, social behaviors of mom may expose her young lambs to pneumonia-causing pathogens. Sheep are highly social animals, which is one reason why they are so susceptible to disease. Yet, it is unclear if lambs become infected with pneumonia from their mothers or from other ewes and lambs in their nursery groups.

How're we tackling it?

To investigate the influence of mom’s condition and behavior on lamb survival we will pair information maternal condition and behavior with lamb survival.

Cause-specific mortality of lambs: Each spring, we will capture, GPS-collar, and monitor survival of lambs born to GPS-collared ewes. Each mortality will be investigated to determine the cause of mortality (e.g., disease, predation, starvation, etc.).

Pathogen detection in mom and lambs: We will use nasal and tonsil swabs from both mother and fawn to detect presence of pneumonia-causing pathogens.

Maternal nutritional condition: We will evaluate nutritional condition of pregnant ewes using ultrasonography to measure fat before birth in spring.

Fall recruitment: We will determine recruitment of lambs that survived until autumn, by relocating GPS-collared lambs and observing uncollared lambs.

Behavior: We will evaluate behaviors of both mother and lamb(s) using GPS locations collected from their collars.

What are our findings?

What's the issue?

Lamb recruitment can be a limiting factor in population growth, especially after a pneumonia outbreak. Immunities gained from mom could increase their chance at survival, but it is unknown if mom can, indeed, pass such immunities on to her offspring.

How're we tackling it?

We will compare serum collected from mothers and their fawns to detect immunities (i.e., antibodies) for various pneumonia-causing bacteria. Since, the blood is collected from the lambs when they are less than 2 days old, we can assume any immunities they have are transmitted from their first drink of mom’s milk.

What are our findings?

We still collecting and analyzing these data.

What's the issue?

Research often leads managers to root issues within a population, however identifying solutions can be an entirely new project. Various efforts for habitat treatments that enhance forage for wildlife, such as prescribed fire in bighorn sheep habitat, are often implemented to bolster wildlife populations. Yet, the efficacy of such treatments often go untested. Testing the efficacy of habitat-enhancing treatments for bighorn sheep is needed information for guiding effective habitat management that promotes robust bighorn sheep populations.

How're we tackling it?

We have installed three habitat exclosures in alpine sheep habitat. Each exclosure contains burn and grazing treatments, as well as combinations of the two. We will monitor the responses of the alpine to these treatments over 3-years following the treatment.

What are our findings?

Treatments were implemented in summer 2018, and we will continue to monitor the outcomes.

People working on the project:

Rachel Smiley, Brittany Wagler, Aly Courtemanch, Greg Anderson, Tony Mong, Hank Edwards, Doug McWhirter, and Kevin Monteith


Wyoming Game and Fish Commission, Wyoming Governor’s Big Game License Coalition, WWNRT, BLM, Wyoming Wildlife/Livestock Disease Research Partnership, Animal Damage Management Board, National Wild Sheep Foundation, Wyoming Wild Sheep Foundation


Publications from this research to come...

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