Hidden costs of disease to greater Yellowstone elk

Brucellosis reduces pregnancy say USU ecologists

Date:  October 29, 2018

Source:  S.J. & Jessie E. Quinney College of Natural Resources, Utah State University

For decades researchers have known that a bacterial disease in elk, bison and cattle in the Greater Yellowstone Ecosystem causes periodic abortions in these animals and chronic illness in humans drinking infected cow's milk. The disease, called brucellosis, poses a financial concern for dairy producers and cattle ranchers, but its effects on the wild elk population have generally been considered minor.

In recent years, however, elk pregnancy rates have become the subject of controversy. Various researchers claim that stress caused by fear of wolves and nutritional deficiencies caused by drought can explain low pregnancy rates in specific elk herds, but until now the effects of brucellosis on elk pregnancy have not been scrutinized.

Utah State University researchers Gavin Cotterill and Johan du Toit report that by mid-winter, elk that test positive for brucellosis are less likely to be pregnant than healthy elk, independent from the abortions caused by that disease later in the year. Cotterill and du Toit, along with colleagues from the Wyoming Game and Fish Department, US Geological Survey Northern Rocky Mountain Science Center, and University of California Berkeley, discuss their findings in Ecology and Evolution published 28 October 2018.

"Mid-winter elk pregnancy rates are often seen as an indicator of an elk herd's health and viability," says Cotterill, a PhD candidate at USU and lead author of the paper. "If we're interested in figuring out the effect that predators or climate are having on elk we need to also account for disease."

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