Winter riskiest time for elk disease transmission

Diseases that can spread between livestock and wildlife include anthrax, bovine tuberculosis, brucellosis and worms

Wildlife can spread disease to cattle and a recently completed study on southern Alberta elk has shed light on the issue.

University of Alberta researchers studied the movement of radio-collared elk and correlated it with the locations of cattle herds grazed by 16 cattle ranchers in the province’s southwestern region.

They concluded that the risk of disease transmission from elk to cattle and cattle to elk was highest in winter, when the two species are in closer proximity and attracted to feed stores, salt and mineral blocks.

“One of the biggest risks to the livestock industry is the transmission of disease from wildlife to livestock,” said U of A biological sciences professor Mark Boyce.

“There is a long list of diseases that occur between livestock and wildlife, including anthrax, bovine tuberculosis, brucellosis and many species of worms.”

Recommendations from the study include pasture management to minimize contact between cattle and wildlife and keeping cattle near farm buildings in winter and in calving season.

“Our study is done in southwestern Alberta where the elk are highly migratory. Most of the elk migrate up into the mountains during the summertime, where there’s very little contact with livestock but the big time of risk of transmission is right now, when the elk and cattle are both on the winter ranges,” Boyce said in an interview.

“If we can reduce the contact between the two species, we can reduce transmission of a long list of diseases.”

Boyce said ranchers in the region who were part of the study tended to have more concerns about livestock predation than about disease issues, although elk damage to stored feed is an irritant.

Small wonder, given the U of A study identified six elk herds in the region and estimated the herd sizes. An elk herd in the Whaleback region is estimated to have 700 to 1,000 animals. Another around Waterton has about 900 animals and a third in Castle-Carbondale has 500 to 700 animals.

The other three are in the Porcupine Hills (450 to 700 elk), Livingstone (340) and Beauvais Lake (150-250.)

Within those herds were more than 150 collared elk that enabled researchers to closely track herd movements.

“Elk are doing really well,” said Boyce. “I would say over the last 20 years, we’ve seen an increase year after year in the number of elk and the number taken by hunters and their distribution has expanded as well.

“I think that people don’t maybe appreciate some of the disease risk issues.”

Within the same study region as the elk herds, researchers estimated there are about 84,000 beef cows in 700 cow-calf operations.

In their paper about the study on integrating livestock management and telemetry data to assess disease transmission risk between wildlife and livestock, researchers Boyce, Mathieu Pruvot, Marco Musiani, Susan Kutz and Karin Orsel said risk of disease transmission in fields peaked in fall when they were used for swath grazing. Elk visits to haystacks naturally peaked in winter when snow was deep.

Higher inter-species contact in winter is relevant when it comes to transmission of illness. Risk of brucellosis and other diseases depends to a large degree on how long pathogens survive in the environment, which varies widely.

As well, different diseases have different methods of transmission, ranging from direct contact with placental matter, in the case of brucellosis, to transmission through contact with feces, urine and saliva.

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