The Western Association of Fish & Wildlife Agencies (WAFWA) Protocol to Improve the Health Monitoring of Bighorn Sheep and the Role of the CWHC

Photo: Peregrine Wolff, Nevada Department of Wildlife

Bighorn Sheep in Western Canada

Bighorn sheep (Ovis canadensis), are regularly regarded as the face of the North American Rocky Mountains. Fossils discovered in North America date back 100,000 years and today bighorn sheep are found in Mexico, the United States, and Canada. There are two subspecies inhabiting British Columbia (BC). California bighorn sheep (Ovis canadensis californiana) inhabit the southwest interior of BC, extending south along the eastern ranges of the Coast and Cascade mountain ranges into northern California. Rocky Mountain bighorn sheep (Ovis canadensis canadensis) are geographically separated from the California subspecies by several interior ranges west of the Rocky Mountains. The Rocky Mountain subspecies inhabits the Canadian Rockies of BC and Alberta (AB) and are found in their native range as far south as New Mexico. Beginning in the early 1900s correlations were made between increasing numbers of domestic sheep flocks and bighorn health issues associated with mortality and population declines. The subsequent recovery of bighorn sheep in western North America is a long but successful story with significant research and management effort to fully understand the health challenges behind the recovery.

The WAFWA Bighorn Sheep Health Monitoring Guidelines

The Western Association of Fish and Wildlife Agencies (WAFWA), established in 1922, includes many committees with membership from wildlife agencies in the western US and Canada including the Wild Sheep Working Group (WSWG) and the Wildlife Health Committee (WHC). These members, along with academic researchers and non-governmental organizations, are collaborating on solutions to the unique health challenges faced by wild sheep.  Research and guidance documents, including dynamic herd health assessment recommendations to allow standardized health assessments of live and dead wild sheep are assisting management agencies in sustaining sheep herds on the landscape. Wild sheep herd health monitoring recommendations, first released in 2009 and updated in 2015, were developed by WAFWA’s Wildlife Health Committee, with members from ten western US states and two Canadian Provinces (BC and AB). The goal of the recommendations is to standardize and encourage wild sheep herd health surveillance done by government wildlife management agencies, including provincial agencies in BC and AB that the CWHC works with to facilitate surveillance efforts.

The CWHC Alberta node follows a protocol based on the WAFWA recommendations and developed in conjunction with Dr. Margo Pybus of the Alberta Provincial Wildlife Disease Unit. The protocol, implemented since 2014, is applied to all bighorn sheep submitted generally through AB provincial wildlife biologists, Fish and Wildlife Officers, Conservation Officers and Parks Canada staff. Routine diagnostic testing achieved through submission of samples or whole specimens to the CWHC for full necropsy undergo a series of five different tests on tissues from various regions of the body. A mineral panel is run on the liver to assess the overall nutritional health of each animal. A series of pooled tissues from major organs that are known be affected by diseases common in bighorn sheep, (mainly respiratory diseases) are submitted for general bacterial culture. More specific testing to survey for Mycoplasma bacteria, bovine herpes virus (BHV-1), parainfluenza virus (BPIV-3), and bovine respiratory syncytial virus (BRSV) is also done. Lastly, feces and other tissues are submitted for culture of Mycobacterium avium paratuberculosis (MAP) the causative agent of Johne’s disease, a resilient and slow growing bacterium.

CWHC –Alberta Bighorns Handled as per the WAFWA Protocol

The described sampling protocol to date has been applied by CWHC-Alberta to 20 bighorn sheep carcasses submitted for necropsy since 2014. The primary cause of mortality was vehicular collision; however, several sheep died from bacterial infections.

Motor vehicle collisions with wildlife can be facilitated by underlying causes in the health of the animal, thus disease surveillance helps to monitor the overall health of a population independent of the primary cause of death. Many wildlife disease-monitoring data sets are skewed to favor motor vehicle collisions, as these are the animals most accessible to wildlife staff. Animals which have died of natural causes are often much harder to locate and many often go unreported.

Mineral panels testing for deficiency or toxicity of macro and trace minerals were done on 15 of the 20 cases (75%). A common trend in 12 of 15 (80%) sheep was a deficiency in one or more of copper (Cu), manganese (Mn), and selenium (Se). Similar findings have been documented for many years, which may be compared in the future with similar data collected in BC. There may be natural deficiencies of these minerals in many areas of western Canada, including mountain soils creating interactions among trace minerals that influence their absorption in the sheep, or other factors.

General culture to grow bacteria present in submitted tissues is next outlined in the surveillance protocol. Of 16 animals with tissues submitted for culture, 11 (69%) cultured one or more bacteria species. The isolated bacterial species were attributed to post mortem overgrowth and not identified as affecting the health of the sheep submitted for necropsy. Specific bacterial culture for the respiratory pathogen Mycoplasma ovipneumoniae (M. ovi) was performed on 13 sheep, all of which returned negative results. M. ovi has been implicated as the inciting cause of severe pneumonia causing large-scale, non-age specific bighorn sheep die-offs. The syndrome is the single largest obstacle to wild sheep management in North America. The pathogen can be transmitted from domestic sheep in which it can reduce weight gains and generally causes a mild disease. After a die-off, lamb survival can be reduced for several years and so pneumonia outbreaks can have a catastrophic effect on bighorn sheep population numbers. Some survivors of outbreaks, particularly ewes may carry the M. ovi in their upper respiratory tracts pass it to their lambs, resulting in their deaths from pneumonia at an early age. This long-term effect highlights the importance of health surveillance to detect the presence of this important pathogen in wild sheep in Alberta.

In addition, molecular testing for the three viruses (BHV-1, BPIV-3, and BRSV) associated with widespread respiratory disease and reduced reproductive success in domestic livestock was done on 14 sheep, with all results coming back negative. Bighorn sheep are also tested for a chronic bacterial infection of the intestines called Johne’s disease. This is similar to Crohn’s disease in people and leads to chronic enteritis with loss of condition and eventual wasting and death.  In total 18 of the 20 sheep were tested for Johne’s disease (MAP). To date, 16 of those 18 (89%) tested negative for presence of the bacteria and two animals have results pending.

Passive surveillance on wildlife submissions in general is extraordinarily valuable in gathering data on the disease status and the general health of a population. Herd level findings such as mineral deficiency in the wild sheep of Alberta is valuable information that is provided to wildlife management teams tasked with maintaining healthy sheep populations. Such information may have not been discovered if not for standardized health assessment protocols such as the one based on the WAFWA Wildlife Health Committee’s recommendations. Use of this protocol across multiple jurisdictions increases the value in such surveillance data and allows wild sheep managers to collaboratively view a broader picture of bighorn sheep health. Comparisons can then be made, hopefully resulting in better management tool development to maintain healthy wild sheep.