BLM-Idaho > Wildlife > Bighorn sheep  ♦  Rangeland Management

Mannheimia haemolytica, the microbe that causes pneumonia in sheep and cattle


Scientific studies have recognized the risk of domestic sheep (or goats) transmitting disease to wild sheep. Wild sheep can also transmit disease to domestic animals, but domestic animals are generally more resilient to diseases, because of breeding, selection and husbandry practices. 

The recommended way to reduce the potential for disease transmission is effective separation – keeping wild and domestic sheep (and goats) apart in time and/or space.

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The BLM manages grazing permits in bighorn sheep habitat on public lands on a case-by-case basis.  In some situations, the permitee can use best management practices (BMPs) to ensure effective spatial separation. For its part, the BLM also adjusts the terms and conditions of grazing and trailing permits to ensure effective — mainly temporal — separation. The agency is also responsible for monitoring the effectiveness of BMPs where they are in use on allotments it administers.

red graphic dot EFFECTIVE Separation

bighorn sheep

Maintaining separation does not necessarily require complete removal of domestic sheep or goats from grazing allotments. Cooperation and communication between the land management agency and a permitee can allow both domestic and wild sheep to use a particular area, either at different times (temporal separation) or at sufficient distance from each other (spatial separation) or both.

sheep with guard dogs

The environmental impact statement (EIS) analyzing impacts of renewing livestock grazing permits on 25 allotments in the Owyhee Field Office (far southwestern Idaho) uses GIS-based modeling to analyze the risk that bighorn sheep from a particular herd will contact an allotment where domestic sheep are authorized to graze or a route where domestic sheep are trailed to or from pastures in-season. 

The model depicts the probability that bighorn sheep moving out of their core home ranges – activity called foraying – will reach a particular grazing allotment or trailing route in the project area. 

three bighorn sheep high on a sunlit ridge

Analysis in the EIS is based on best available science, which suggests that contact between bighorn sheep and domestic sheep can transmit disease, causing mortality to individual sheep and reducing longer-term herd health.  The Idaho Dept. of Fish and Game identifies disease transmission as a key factor in determining the viability of Idaho's bighorn sheep. 

Alternatives for managing the risk of contact are analyzed in the EIS, and the record of decision (ROD) for any permits issued for allotments or trailing routes where disease transmission may be a concern will detail actions to be taken to manage that risk.