Wyoming Game and Fish will continue using a brucellosis vaccine on elk even though the agency’s research says it has not stopped brucellosis-induced abortions and may increase the percentage of elk testing positive for the disease.
Game and Fish officials confirmed the research findings last week and also committed to at least another winter’s worth of inoculating elk with the vaccine Strain 19. While the latest research says Game and Fish can’t find a statistically significant benefit from the vaccine across the entire Wyoming elk population, some believe it may prevent a small number of “reproductive failures.”
That’s one reason to continue with the vaccine program, Game and Fish Wildlife Division Chief Brian Nesvik said.
“This one analysis certainly isn’t enough to discontinue a program we’ve used for years,” he said. “There are indications it reduces abortions. If there’s effectiveness, even in small areas, it’s worth continuing.”
Game and Fish has used Strain 19 for 29 years to inoculate 100,000 Wyoming elk against brucellosis. During that period there’s been substantial doubt whether Strain 19 works when elk are inoculated by “bio bullet” delivered by an air rifle — the way it is applied on 18 of 22 Game and Fish feedgrounds.
Wyoming feeds about 16,000 elk each winter. Brucellosis is suspected of reducing elk productivity by some 21 percent and can be passed to cattle with significant consequence to stockmen.
Lab studies don’t translate to the field
Controlled laboratory-type studies show the vaccine will “modestly reduce” abortions in elk, the principal vector of brucellosis. Whether it has an effect when used at feedgrounds was previously unknown.
“No field study [until now] has assessed efficacy of the s19 program based on abortions,” Game and Fish biologists wrote in summarizing agency work in the Sublette County area during 2013. That report, for the first time, crunched numbers from eight years of field research on elk abortions.
The field research compared the rate of abortions between vaccinated and unvaccinated elk. The Dell Creek feedground near Bondurant has acted as a “control” feedground at which elk have never been inoculated.
Elk are generally loyal to their home feedgrounds, a fact that gives the comparisons some level of relevance. Game and Fish has information on herds that were completely inoculated, not vaccinated at all, and partially vaccinated, referred to as “levels of coverage.”
“Based on these analyses, the s19 program has not affected … abortion rate at the population level,” the report said. “Despite the use of s19 or levels of coverage, numerous abortions continue to occur on feedgrounds allowing the disease to perpetuate in elk.”
The report also suggests the vaccine may increase the portion of elk that test positive for exposure to brucellosis. There’s no way to actually determine whether an elk has the disease without killing it. Blood tests revealing exposure are the next best method.
Game and Fish has information from before inoculations began as well as since. It also has data from the control feedground and the 21 others.
That allowed biologists to compare the rate of positive blood test results — known as seroprevalence — among various groups of elk.
Biologists compared seroprevalence from before the inoculation program began with those collected after. They also compared seroprevalence between inoculated herds and the herd at the Dell Creek control feedground.
Comparisons focused on yearlings and adult females. The Greys River feedground near Alpine figured as an important one in studies because vaccinations there have been going on the longest and because inoculation coverage is excellent.
“Paired data for yearlings … and adults … from 1998-2013 show no difference between mean seroprevalence of vaccinated Grey’s River and unvaccinated Dell Creek populations,” biologists wrote. “Among all feedgrounds from 1971-2013 for yearlings, seroprevalence prior to and following inception of s19 suggests that seroprevalence has not been lowered by s19.”
Use of the vaccine may have even increased the amount of positive blood tests, the report says.
“Among all feedgrounds from 1971-2013 for adults, seroprevalence prior to and following inception of s19 suggests that seroprevalence has been not lowered but rather raised by s19,” the report says.
The effect of Strain 19 in the field on abortions was a looming unanswered question about the vaccine, said Brandon Scurlock, head of the Game and Fish brucellosis program who works in Pinedale. Laboratory experiments showing modest results needed to be confirmed in the field.
“We’re trying to get them to stop aborting,” he said. “We wanted to see if there’s an actual difference in abortion rates,” between vaccinated and unvaccinated elk.
Research follows elk births, abortions
Researchers used vaginal implant transmitters to find live or dead elk calves following delivery. Vaccinated elk showed a 16 percent abortion rate while unvaccinated elk aborted 22 percent of the time.
“There is a couple fewer,” among vaccinated elk,” he said. “It’s not statistically significant.
“It’s most likely preventing a few (abortions), even if it’s not statistically significant,” he said of Strain 19. “Likely it’s reducing them by just a couple.”
Some argue that preventing one elk abortion could be worth it, especially if that abortion happened when an elk had wandered to a cattle feed line, Scurlock said.
“If it is preventing just a few abortions, maybe its worth it — that’s the argument,” Scurlock said. “I don’t know the answer to that discussion.”
Even with 9 years of data (2014 results were not included in the report) the sample size is small enough to make Scurlock and others question the results. Of 505 transmitters implanted in pregnant elk, only 30 revealed reproductive failures.
“There are some sample-size issues,” he said. “Ideally you’d bump that up to 100 reproductive failures.”
Researchers are “a little bit wary about [the] sample size,” he said. Nevertheless, “It’s the biggest data set that’s out there.”
For Nesvik, the numbers are no reason to cut the program. One research paper, co-authored by Scurlock, calculated costs of Strain 19 vaccines at $23,000 a year.
“There’s not a consensus on its effect,” Nesvik said of Strain 19. “There are some folks that have different opinions.
“Even our own blood tests have some issues,” Nesvik said of the byzantine world of brucellosis research. “The analysis does have some noise,” or uncertainty.
Preventing one abortion could be significant, he said. “It can have a huge impact on an elk that aborted on private land.”
That’s because draconian agriculture rules call for the slaughter of cattle herds exposed to the disease. Although stockmen and women are reimbursed with federal funds, “depopulation” can upend generations of selective breeding and record keeping at cow-calf operations.
Given that and other factors, “I think it’s worth continuing,” Nesvik said.
A persistent bacteria
The findings and uncertainties provide a window into the disease, a bacteria, that was originally imported from Europe in domestic cattle. The U.S. Department of Agriculture has tried for decades to eradicate it.
Brucellosis is why milk is pasteurized. It can cause troubling undulant fever in humans, which is almost impossible to cure.
Game and Fish wildlife disease specialist Hank Edwards in Laramie underscored the challenges.
“It’s very difficult to get a good handle on efficacy of Strain 19 in a wild population,” he said. “There are so many variables you have no control over. It’s much easier if you have a pen full of cattle and vaccinate and watch what happens.”
Close contact on winter feedgrounds allows diseases to spread faster. But seroprevalence also has increased among elk that do not winter on feedgrounds.
Game and Fish does not feed east of the Continental Divide. Elk in the Cody area, where there is no feedground, have shown elevated seroprevalence, perhaps because elk on private land there also mingle closely in winter.
“It takes a very long time to determine whether that vaccine is effective,” Edwards said. “There still is a question — ‘at what point do we say we’re sure that Strain 19 is not worth pursuing?’
“I don’t know the answer to that question,” he said. “There’s still a significant number of people in our department and the ranching community that feel (Strain 19 is) still effective and needs to be pursued.”
“For a disease we’ve been studying so long, we don’t know shit about this,” he said.
While Game and Fish continues shooting bio bullets, it faces another challenge. The bio bullet will soon be unavailable from its manufacturer, Nesvik said.
“The company that is the only company that makes the bio bullet and the gun is going to go out of business or is going to quit making those bio bullets,” he said. Whether Wyoming will take over that manufacturing task or seek another maker is up in the air.
“We’re in the process of discussing that issue,” Nesvik said. Meantime, “we have enough bio bullets and vaccine to do it this winter.”
Research and development continues, including work on a freeze-dried form of Strain 19 delivered by biodegradable dart, Nesvik said. Game and Fish employs other strategies to reduce infections.
Those include improving natural habitat and ending feeding as early as practical in an effort to spread elk out when they are most likely to abort. Protecting scavengers like coyotes on feedgrounds also helps reduce brucellosis because they scarf up aborted fetuses, reducing the chance of the disease spreading.
A simple effort — spreading elk out when they are being fed — shows promising results. A paper co-authored by Scurlock and published in the Journal of Wildlife Management in 2012 shows that low-density feeding reduces elk contact with aborted fetuses by more than 70 percent.
Game and Fish began experimenting in 2008 with low-density feeding at five feedgrounds. The practice requires more time and work from feedground staff.
“Managers should consider implementing (low-density) feeding throughout Wyoming’s feedground system and in other western states where regular or emergency feeding of elk still occurs and may exacerbate the transmission of diseases,” the 2012 Journal of Wildlife Management article by Scurlock and others recommends. “Low-density feeding is likely to reduce (brucellosis) transmission with negligible effect on the total cost of feedground operation.”
Most efficient strategy?
It’s the most cost-effective method of reducing the brucellosis threat, according to a separate research paper, “Cost-benefit analysis of a reduction in elk brucellosis seroprevalence in the southern Greater Yellowstone Area.” That review, also co-authored by Scurlock, additionally suggests implementing “inexpensive cattle management strategies” including hazing elk from cattle feedlines and giving adult cattle booster vaccines.
Operating feedgrounds themselves reduces the time fed elk spend on on native range and cuts down on the nutrition they get naturally, researchers said in yet another paper published by the Ecological Society of America. Compared to unfed elk, those from winter feedgrounds migrated 12 miles less, got to summer range 5 days later, stayed there almost a month less (26 days) and left 10 days earlier in the fall.
Feeding “disconnected migration by fed elk from spring green-up and decreased time spent on summer range, thereby reducing access to quality forage,” the paper said. Scurlock, along with University of Wyoming researchers and others co-authored “Supplemental feeding alters migration of a temperate ungulate.”
Wyoming operates feedgrounds “To maintain (Game and Fish) Commission population objectives and control elk distribution in an effort to minimize conflicts with human land uses,” the agency says. The feedground program cost $2.1 million in FY 2013, according to an annual report to the commission, the latest one available.
That report estimates there are 112,000 elk in Wyoming. Hunters slayed 26,365 in 2012.
License revenue generated $9.3 million, the report says, and other program sources added $8.7 million for a total of $18.21 million in revenue. The elk program cost $14.7 million that year.
Elk hunters spent $49.9 million in 2012, the report said. The program cost $558 per animal and generated $1,856 in “economic return” per wapiti.
° Download the pdf of the Brucellosis/Feedground/Habitat appendix to the Pinedale Region 2013 elk “job completion report.”
° Download the pdf of the paper “Cost-benefit analysis of a reduction in elk brucellosis seroprevalence in the southern Greater Yellowstone area.”
° Read the Journal of Wildlife Management article about low-density feeding.
° Access the latest paper on feedgrounds’ effect on migration, “Supplemental feeding alters migration of a temperate ungulate,” at this website.