Some Deadwood bighorns testing positive for deadly bacteria

Several bighorn sheep from the Lead-Deadwood herd have tested positive for a pneumonia-causing bacteria that has decimated some herds throughout the West. Pioneer photo by Vicki Strickland

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DEADWOOD — Across the West, a pneumonia-causing bacteria has wreaked havoc among bighorn sheep herds in numerous states, including South Dakota.

In 2004, the Custer State Park bighorns contracted mycoplasma ovipneumoiae, the pneumonia-causing bacteria that killed 70-80 percent of the park’s 200 sheep.

It is also in the Black Hills herd, found near Rapid City, and now the state’s newest herd, located in the Lead-Deadwood area, have animals testing positive for the pathogens.

Since October, six sheep in the herd have died to various injuries or causes. Of those six, three have tested positive for mycoplasma ovipneumoiae. A fourth is expected to test positive.

“We definitely have the pathogens in the herd that causes pneumonia. What we haven’t had is a mass die-off. So far, it appears to be a few individuals that have tested positive for it,” said John Kanta, regional terrestrial resources supervisor for the South Dakota Game, Fish, and Parks.

Where or how they are picking up the pathogens is unknown.

“We’re scratching our heads. We don’t know,” Kanta said. “That is part of what we are doing right now, too, trying to determine where that risk is.”

The 26 sheep, when they were captured in February 2015 in Alberta, Canada, prior to being relocated to South Dakota were tested for a variety of diseases, including for mycoplasma ovipneumoiae. All tests were negative.

Wildlife managers know wild sheep can acquire the pathogens from domestic sheep and goats, but there has been no known contact with domestic animals, with one exception. That occurred last fall when the herd’s 2-year-old ram ventured out of the Black Hills and came into contact with sheep near St. Onge.

In accordance with department policy, that ram was killed before it came back into contact with members of the herd. Even then, the ram tested negative for the pathogens.

Kanta said it is concerning that the new sheep are testing positive. A planned augmentation to the herd in the next year or two is now on hold until the animals do not test positive for the pathogens.

The first sheep to die recently was on Oct. 13, when it fell from a cliff. A second died on Oct. 29 and tested positive for mycoplasma ovipneumoiae. It had a neck injury but the exact cause of death was unknown.

On Nov. 3, another sheep tested positive. It was one of the herd’s oldest ewes and had an infection of the upper jaw.

On Nov. 7, a sheep in the isolated Gilt Edge herd, a breakaway group of six animals from the Lead-Deadwood herd, drowned in one of the mine’s ponds. The animal was too far decomposed to be tested.

The same week another animal was injured and euthanized. It too tested positive.

The sixth animal, appeared to be sick and was euthanized on Nov. 15. Tests are not yet back, but Kanta said he anticipates the ewe to test positive.

“So far we haven’t documented any sheep dying because of the pneumonia. We are finding sheep that have been hit by vehicles, or had injuries, then when we test them, they tested positive,” Kanta said.  

Kanta said there have been instances in other states where herds that have acquired the mycoplasma ovipneumoiae have had a portion of its herd die off.

A new study with the Custer State Park and the Black Hills herds is showing promise. Both herds have individual animals that test positive for the pathogen. Last winter, the GF&P captured every sheep in both herds. Those that tested positively for shedding the pathogen were removed from the Custer herd as the treatment group. All animals in the Black Hills herd were released as the control group.

This spring, nine lambs were born in Custer State Park and all but one have survived. The lone lamb that died did not die from the pneumonia.

In previous years, before the “shedders” were removed, nearly all lambs died.

“So far we are seeing really good results, and it appears as if this is something that would work,” Kanta said of removing selected sheep from the herd.

Unfortunately, the only way to test the animals is to capture them and swab their nose and throats.

Aside from the few animals testing positive for the pathogens, the 34 animals in the Lead-Deadwood herd are doing well. Five lambs were born this spring, down from 13 last spring. But Kanta said this was expected since the only rams in the herd are young and are not as successful in breeding as the older, mature rams.

“Our expectation this year is breeding should be better this year,” he said.

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