Frozen deer heads thaw on a table as DNR lab workers process others. David Kenyon, Michigan DNR photo
January 01, 2012One of Department of Natural Resources' biggest, yet least publicized, operations is cranking at high gear right now as deer season heads into the home stretch.
The DNR's Wildlife Disease Laboratory is processing deer heads, examining lymph nodes and checking for signs of bovine tuberculosis and chronic wasting disease in the herd.
"We'll process about 6,000 heads, a little over 5,000 for TB and about 1,000 for CWD," said Steve Schmitt, a veterinarian with the Wildlife Division. "That's our goal.
"That's down from the peak; at one time we were doing about 25,000 for TB and 4,000 to 5,000 for CWD."
The DNR is able to get adequate information about the diseases by concentrating its efforts on deer killed in geographic areas where the problems have occurred.
"We can do fewer now by concentrating our efforts," Schmitt said. "We're still looking all over the state, but our intensive surveillance is obviously where we found TB and CWD in the past – the northeast Lower Peninsula for TB and basically Kent County and the surrounding counties for CWD."
Most of the heads that make it to the "head shed" – as DNR staffers have nicknamed the facility located at Michigan State University's Diagnostic Center for Population and Animal Health – come to the DNR from deer check station.
"At check stations we get basic biological information that we use to manage deer – age, sex, beam diameter of the antlers – but depending on where it's coming from in the state, we may want the head for CWD or TB testing," Schmitt explained.
"It's all voluntary – both checking the deer and letting us have the head for disease testing," he continued. "If a hunter's willing to give us the head and it's from a county we want, our folks scan the hunting license and the CWD or TB tag, linking them together in the electronic data base – with all the information, like township, section and range where the deer was taken – and we've got all that information before we see the deer head."
DNR staffers collect deer heads from check stations and truck them to East Lansing for testing. The first step in the process to age the deer – by looking at tooth wear, just as is done at the check station, to see if they have the same age estimate. (Most of the time, they do.)
"It's very important to have an accurate age for our disease models to make estimates of disease transmission rates," Schmitt said. "For example, the percent of positive heads among 1 ˝-year-old deer gives you an indication of the transmission rate, because we know they got the disease within the last year and half.
All heads are tested for TB while a smaller subset is tested for CWD.
Other deer that the DNR obtains in other ways, however, are also tested for CWD. For instance, if someone calls and reports a deer exhibiting neurological systems indicative of CWD, the DNR will either send a staffer to dispatch the deer or ask the landowner to shoot it and then will collect the carcass.
"Those are by far the most important animals to test for CWD," Schmitt said. "In states like Colorado, where they have a lot of CWD, deer that are showing neurological systems are 11 times more likely to be positive for CWD than an ordinary hunter-harvested deer."
Road kills are often tested for CWD, too.
"A deer that has CWD is more likely to walk out in front of a car and get hit than a healthy deer," Schmitt said.
After the deer are aged, lab workers cut into the six lymph nodes (three pairs) in the head, and examine the lymph nodes for abscesses, pus, lesions – any abnormality.
"If we don't find anything, it's negative," Schmitt said. "But if we find something, the lymph node is collected and parts of it are sent to the MSU Diagnostic Center and the Department of Community Health."
The suspect nodes are subjected to a number of tests.
"And even those that appear negative on further examination are cultured for six to eight weeks because bovine TB is caused by slow-growing bacteria."
Most of the work at the shed is performed by full-time DNR lab staffers, though the USDA's Wildlife Services division sends folks over to help, too.
"We're seeing about the same number of suspects as we have in the past from the same places we've seen them in the past," Schmitt said. "TB prevalence has been just under 2 percent for the last seven years.
"To a lot of people, it's not that big an issue – the prevalence rate is not that high and it doesn't kill a lot of deer. But to the cattle producers and the Michigan economy, it is a big deal."
Models indicate that Michigan's TB prevalence rate in the infected area is likely to remain static for decades, Schmitt said.
"If deer numbers stay where they are and feeding and baiting remains under control, it shouldn't get any worse," Schmitt said. "But if we want to bring prevalence down, we're going to have to be much more aggressive with our management – we'll have to bring deer numbers down and get more aggressive on the feeding and baiting bans.
"We're still the only place in the world where bovine tuberculosis has become established in the wild deer herd."
To learn more about the health and management of Michigan's deer herd, visit www.michigan.gov/deer.n