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.

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.

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.

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.

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.

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.

Project leads

Rachel Smiley

Brittany Wagler

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.

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.