Cooperative Fish and Wildlife Research Units Program: Montana Wildlife
Education, Research and Technical Assistance for Managing Our Natural Resources

Many bighorn sheep populations across the West are struggling with population numbers that are stagnant to decreasing. The cause of this poor population performance can generally be attributed to effects of bighorn sheep respiratory disease. The major causative agent of primary atypical pneumonia in bighorn sheep is Mycoplasma ovi pneumoniae (M. ovi). The disease usually expresses itself as an all-age die-off within a newly infected herd. Subsequently, years to decades of poor lamb survival occur with lambs dying of pneumonia. This mortality prevents the population from rebounding after the initial infection of the herd and is a major concern for managers trying to restore the vigor of the herd.

The purpose of this project is to test the efficacy of management actions designed to improve performance of struggling bighorn sheep populations by increasing lamb survival and ultimately ensure the conservation of the species. To that end, we will evaluate the effects of testing and removal of M. ovi positive animals. This management strategy is based on the theory that only a few individuals within the herd serve as chronic shedders of M. ovi, and they maintain and pass the pathogen on to doomed naïve lambs born each year. By identifying these few individuals and removing them, we will improve lamb survival. This strategy has been successfully demonstrated in other herds across the West in both free-ranging and captive herds, and during this project we will apply it in the Highlands Sheep herd in Montana.

We will also explore the impact of mineral supplementation on lamb survival and population growth. Many bighorn herds demonstrate trace mineral deficiency (based on domestic sheep reference standards). Of particular interest is selenium which has been linked to immune function. The hypothesis we will test is whether access to mineral supplements will increase lamb survival by providing a more robust immune response to M. ovi and other respiratory pathogens.

Thus, the overarching goal of our research is to explore whether management actions to improve the health of bighorn sheep herds will be successful.