One infected animal.
That’s all it took to launch one of Canada’s largest bovine tuberculosis investigations in years.
The first question many producers ask when bovine tuberculosis (bTB) is detected is whether wildlife brought the disease onto the farm. Yet in Canada’s recent investigations, regulators have been unable to link the cases to wildlife.
Hundreds of miles away, Michigan veterinarians face the opposite reality. There, controlling bovine tuberculosis begins with managing infected white-tailed deer.
The difference isn’t the pathogen. It’s where the pathogen survives. That single distinction changes nearly every aspect of a bTB control program, from where surveillance occurs to the questions investigators ask after a positive test.
Recent presentations by Dr. Noel Ritson, veterinary program manager with the Canadian Food Inspection Agency, and Dr. Nora Wineland, Michigan state veterinarian, offered a unique look at how neighboring regions are tackling the same disease under very different circumstances.
Every bTB control program is designed to interrupt transmission. When the disease exists only in cattle, investigators focus on tracing animal movements and eliminating infected herds. Once wildlife becomes a long-term reservoir, disease control expands beyond cattle to managing interactions between livestock and wildlife.
Strategy 1: Find the Rare Infection
Canada’s bTB eradication program has evolved significantly over the past century. While early efforts relied on routine on-farm testing and removing reactor animals, surveillance now occurs primarily at slaughter facilities, where inspectors identify suspicious lesions that trigger a full epidemiologic investigation.
“We do rely largely on surveillance, and the majority of that surveillance is done within abattoirs,” Ritson says.
That surveillance system was tested in an unusual way over the past three years.
“Getting three consecutive years, ’23, ’24, ’25, where we had positives is a bit of an anomaly and has resulted in a significant amount of work,” he says.
Once an infected animal is identified, investigators trace its movements through auctions, assembly yards, feedlots and breeding herds before locating the herd of origin. The herd is placed under movement restrictions, tested and ultimately depopulated while investigators determine where cattle may have moved before or after exposure.
One assumption frequently arises during these investigations.
“Producers automatically assume this has come from wildlife,” Ritson says. “However, we have not been able to identify any positive wildlife in proximity to any of the recent cases that we’ve had.”
Instead, investigators often find themselves reconstructing years of cattle movements. Every auction receipt, sale record and identification tag becomes another piece of the puzzle.
“Being able to document animal movement can make a huge difference,” Ritson says.
That advice extends beyond maintaining accurate records. During one investigation, Ritson recalled a producer insisting there was no possible way bTB could have entered the operation because it was a “closed herd.” As investigators walked through the operation, however, they discovered feeder cattle were purchased each winter and temporarily commingled with the breeding herd.
The experience underscored an important lesson: Disease pathways are often less obvious than producers believe.
Strategy 2: Manage an Established Wildlife Reservoir
Michigan’s challenge is fundamentally different.
Once white-tailed deer became a reservoir for bTB, eradication was no longer simply a matter of finding infected cattle. Preventing transmission between wildlife and livestock became just as important.
The state’s program combines annual herd testing, movement permits and herd protection plans with intensive wildlife surveillance. Wildlife Services uses forward-looking infrared surveys to identify deer entering cattle operations after dark, allowing producers to target areas where deer and cattle interact.
“We’re working with these herds to do things to keep the deer out of these farms, away from the feed, out of the water sources and get rid of all the attractants,” Wineland explains.
Those efforts include fencing feed storage areas, protecting water sources, removing deer attractants and, when necessary, removing deer that repeatedly visit cattle operations.
The program requires cooperation among multiple agencies, producers and veterinarians.
“It really takes the village in Michigan,” Wineland says.
Why the Playbooks Are Different
Although the challenges differ, both realities point to many of the same practical lessons.
Good records matter. Animal movements matter. Biosecurity matters.
Whether the risk comes from purchased cattle or wildlife, understanding how animals move and interact is essential for limiting disease spread.
Veterinarians also remain central to both systems. Beyond helping producers strengthen biosecurity, practitioners are often responsible for surveillance testing and recognizing suspicious animals before an investigation ever begins.
As Wineland emphasizes: “Anything other than just normal skin when you come back to palpate [after a TB test], we want to hear about.”
An Old Disease That Still Demands Modern Thinking
More than a century after bovine tuberculosis eradication programs began, veterinarians continue to adapt their strategies to meet changing disease risks.
Canada and Michigan may be fighting bTB in different ways, but both programs share the same objective: interrupt transmission before the disease reaches the next herd.
In Canada, that means rapidly detecting rare infections, tracing animal movements and eliminating infected herds. In Michigan, it means reducing opportunities for infected deer and cattle to interact. The strategies differ because the epidemiology differs, but both depend on understanding how bTB moves through a population.
Whether the threat comes from an infected feeder calf moving through multiple auctions or a white-tailed deer slipping into a feed bunk after dark, bTB exploits connections that producers may never notice. The most effective control programs do more than react to positive tests. They identify and close those hidden pathways before the disease has an opportunity to spread.
