Wyoming wildlife scientists are in the early stages of trying to determine if well-fed, healthy bighorn sheep are less prone to contracting deadly pneumonia than sheep in poorer nutritional condition.
The research builds on disease monitoring in the Jackson sheep herd in recent years, and also of herds near Dubois and Cody. The work aims to tease apart why some herds seem to better withstand disease.
On the first leg of a multiyear research project, Wyoming Game and Fish Department officials met Friday with a crew from the Wyoming Cooperative Fish and Wildlife Research Unit. On a clear and crisp morning, a helicopter dangling two sheep approached the researchers near where the western foothills of the Gros Ventre Range terminate on the flats of the National Elk Refuge.
Once the sheep were gently deposited on the ground, the team rushed to the blindfolded ewes. Legs secured with hobbles, the animals were subjected to a series of tests: Girth and lengths were measured, fecal samples were gathered, throats were swabbed for saliva, blood was drawn and each sheep got an ultrasound to measure body fat and check for lambs in the womb.
Assistant Professor Kevin Monteith, with the co-op, ran each ultrasound test.
“You guys see that right there?” Monteith said, gesturing to a transportable screen. “That’s a little ram.”
By the end of the morning, six sheep had been processed at the site. That afternoon more research specimens were gathered in the Gros Ventre. That night the co-op crew headed toward Cody to do it all again the next day.
Great care is given to the bound bighorns while they were being checked. Monteith gave instructions to the crew before the first airship dropped in.
“Our highest priority is taking care of those animals,” Monteith said. “Monitoring temperature closely, trying to keep them comfortable.
“Of course we can talk — we’ll need to relay information — but do our best to keep our voices down and minimize any reactions the animals have,” he said.
Save for several routine cold water enemas to cool overheated sheep, the operation went smoothly.
The data that was gathered will one day help Game and Fish biologist Aly Courtemanch understand what’s going on with the Jackson sheep herd.
This spring Courtemanch counted 319 bighorn in the Jackson herd, up from 268 a year ago.
“It’s definitely recovering from that pneumonia outbreak pretty quickly,” Courtemanch said of the herd in an early March meeting. “I think the population is doing well.”
To account for missed animals, Courtemanch rounded the count up to a herd estimate of 450 bighorns. She also counted 38 lambs for every 100 ewes, a healthy ratio that signifies a growing herd.
The way the Jackson herd is growing, it wouldn’t be a surprise if pneumonia knocked back the population sometime soon.
“It’s hard to say whether there’s truly a pattern yet,” Courtemanch said, “but we have two instances where the population grew to about 500 animals and then went through a pneumonia outbreak.”
The first crash happened in 2001. The herd recovered, grew and then the process repeated in 2011.
“It grew, got close to 500 again, and then crashed,” Courtemanch said. “The way it’s growing, if it stays on that trajectory and if that pattern holds true, we could expect potentially another pneumonia outbreak here in a couple years.”
Pneumonia, which is traced to pathogens carried by domestic sheep, has devastated other Wyoming sheep herds. Over the Continental Divide in the Whiskey Basin, the sheep herd crashed in the early 1990s and never really recovered, Courtemanch said.
Sheep herds in the Cody area, meanwhile, don’t seem to be affected by the same pathogens.
“Cody as far as we know has never gone through a substantial outbreak, Courtemanch said. “They’re carrying all the same bugs, but they seem to be affecting them completely differently. So why is that?”
That’s where Monteith’s body condition tests come in. The study he’s heading, “Unraveling the nutritional-disease interface in population dynamics of bighorn sheep,” will try to determine if healthy sheep are less prone to pneumonia.
“The conventional thinking is that as you get a denser population and more competition for resources, that would probably show up as lower fat levels in females,” Courtemanch said. “Potentially that may trigger a change in the pathogen loads and potentially a pneumonia outbreak.
“We’re trying to figure out that piece to the puzzle,” she said. “No one’s ever looked at that before — how body condition really plays into these pneumonia outbreaks.”
Ideally, the sheep study will be combined with similar research happening in Montana and Colorado for a broad-scale look into the dynamics of bighorn sheep die-offs, Game and Fish disease specialist Hank Edwards said.
“Which pathogens are significant and which pathogens have herd-health problems and which don’t?” Edwards said. “Right now we’ve been chasing pathogens forever.
“There’s lots of factors that lead to die-offs — more than just bugs,” he said. “We need to figure that out. What are those factors, and can we manage to prevent some of those?”