Bighorn Sheep Nutrition Disease

A bighorn sheep ewe in her summer coat lies in front of a few-month-old lamb. They are in a bed of short, alpine plants with large, lichen-covered rocks.
Photo credit: Tayler LaSharr

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 suspect that the susceptibility of a bighorn sheep population to a pneumonia outbreak may be dependent on the nutritional quality of their landscape, and therefore the nutritional condition of the sheep on that landscape. We are studying how disease, habitat, and numerous other factors interact to influence adult and lamb survival.

A close up of a bighorn sheep lamb, just hours after being born. The lamb has a short snout, huge eyes, and tufts of hair sticking out everywhere. The lamb is laying in slushy snow.
Photo credit: Rachel Smiley

Main Questions

A schematic showing the relationship between fat, immune function, survival, and reproductive success in bighorn sheep. In the top part of the schematic, a large arrow points from a fat sheep and connects increased immune function. This then ricochets to increased survival and reproductive success. In the bottom, a narrow arrow emerges from a skinny sheep, connecting to decreased immune function, lower probability of survival, and lower reproductive success.
Diagram credit: Rachel Smiley

How do nutrition and disease affect survival and raising offspring?

To investigate the influence of maternal condition and disease status on survival and raising offspring, we pair information on the nutritional condition and disease status of mom with knowing how long lambs survive after birth.

A bighorn sheep lamb stands on a cliff's edge and looks over a canyon. It looks like their first winter coat is starting to come in.
Photo credit: Brittany Wagler

Do moms transmit disease immunity to lambs at birth?

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 pass such immunities on to her offspring. We are comparing antibodies–a way to measure immunity–between moms and newborn lambs.

Short vegetation in the alpine. There are small rocks and short plants in the foreground, with miles and miles of mountains out onto the horizon. There are no trails, roads, or other obvious signs of humans. The sky is a bright blue with popcorn clouds.
Photo credit: Rhiannon Jakopak

How does habitat quality affect nutritional condition and immunity?

Pneumonia-causing pathogens are present in most bighorn sheep populations in Wyoming, but some populations are more resilient to outbreaks than others. Sheep 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 sheep with limited access to high quality forage.

Field ecologists hike on a trail along a snowy plane. They hike along a forest, with mountains in the background.


A bighorn sheep ewe wearing a GPS collar struts among short alpine vegetation and small granite rocks.
Photo credit: Brittany Wagler

Scientific papers

“Effects of helicopter net-gunning on survival of bighorn sheep” by Brittany L Wagler, Rachel A Smiley, Alyson B Courtemanch, Gregory Anderson, Daryl Lutz, Doug McWhirter, Doug Brimeyer, Patrick Hnilicka, Cody P Massing, David W German, Thomas R Stephenson, Kevin L Monteith. Published 2022 in the Journal of Wildlife Management.

“Heterogeneity in risk‐sensitive allocation of somatic reserves in a long‐lived mammal” by Rachel A Smiley, Brittany L Wagler, Tayler N LaSharr, Kristin A Denryter, Thomas R Stephenson, Alyson B Courtemanch, Tony W Mong, Daryl Lutz, Doug McWhirter, Doug Brimeyer, Patrick Hnilicka, Blake Lowrey, Kevin L Monteith. Published 2022 in Ecosphere.

To see the other scientific papers that have come from this research, visit our list of peer-reviewed publications.

A scientist looks through binoculars at an unknown object. She is smiling. She is standing in a snowy forest, with burned trees covered in snow in the background.
Photo credit: Tayler LaSharr


“Facing a ‘die off,’ bighorn sheep get airlifted for a health checkup,” by Hannah Merzbach for Wyoming Public Media, 2023. Link.

“Bighorns in the Upper Green captured for research,” by Mark Gocke for Wyoming Game and Fish Department, 2023. Link.

“Biologists worry about die-off after ewe hunt failed to substantially cull pneumonia-prone bighorn herd,” by Billy Arnold for Jackson Hole News & Guide, 2023. Link.

“Amidst the rocky crags,” by Emily Reed for Modern Huntsman, 2021. Link.

People gather around a table, where a man is trying to count the number of rings on a sheep's horns to age him.
Photo credit: Rhiannon Jakopak

Outreach and engagement

Each year, we travel to Reno, Nevada, to share our work and talk with sheep enthusiasts at the Sheep Show. We also share our work with K-12 students, whether at camps with the National Bighorn Sheep Center or in classrooms around the state, whenever possible.

Project leads

Jack Gavin

Jack marvels at a small frog.

Rachel Smiley

A scientist with a dirty face, a ball cap, and a puffy jacket stands far away from a female bighorn sheep, who is in the background. The bighorn sheep is looking off into the distance, and seems to not notice the scientist.

Brittany Wagler

Brittany smiles at the camera, gleefully showing off a cylinder of ungulate poop.

Collaborators, partners, and funders

This project is conducted in close collaboration with the Wyoming Game and Fish Department and the Wyoming State Veterinary Laboratory. This project is supported by the Wyoming Governor’s Big Game License Coalition, Wild Sheep Foundation, Wyoming Wild Sheep Foundation, Bowhunters of Wyoming, Wyoming Wildlife Livestock Disease Research Partnership, Wyoming Wildlife and Natural Resource Trust, Bureau of Land Management, Wyoming Animal Damage Management Board, United States Forest Service, Teton Conservation District, United States Fish and Wildlife Service, and Mountain View Resort, Lodging, and RV Park.