On Oct. 8, the Montana Department of Livestock (MDOL) issued a release confirming the detection of a herd infected with bovine tuberculosis (TB) in Blaine County. The confirmation came after extensive testing by MDOL and USDA livestock officials.
Bovine TB is a slow-progressing bacterial disease. Incubation of the disease can range from months to years and cattle often do not show any outward clinical signs. When symptoms do emerge, they are often discreet and present much like any other bovine respiratory illness. Bovine TB is transferred through close, nose-to-nose transmission. It can cross the species barrier and be transferred to humans with the main vector of such a transaction being raw, unpasteurized milk.
Due to its zoonotic potential, bovine TB is a disease that is regulated by the federal government. Although the disease was once more common in U.S. cattle herds, proper tracking and management has reduced its impact and now only about a dozen cattle herds in the country are diagnosed with bovine TB each year.
The current confirmed TB-positive herd is Montana’s first in decades. The initial infected cow was detected at a processing plant in Minnesota during a standard post-mortem meat inspection, which every beef carcass is required to go through. During the inspection, officials closely examine the carcass looking for any abnormalities. The whole purpose of the inspection is to ensure only the safest, most quality meat is allowed into the food system.
“As part of that post-mortem inspection, inspectors at the slaughter plant found an animal with lesions that were abnormal and looked like they could have been caused by TB,” said Dr. Marty Zaluski, Montana State Veterinarian.
Tissue samples were taken from the carcass and sent to a lab to be cultured. After extensive testing it was concluded the cow was in fact infected with TB. From there, officials used ear tags and market records to trace the animal back to its herd of origin in Blaine County.
Confirmation of a bovine TB-positive cow triggers a whole epidemiological investigation. The entire original herd of cows were tested, resulting in the discovery of four more bovine TB-positive animals. Because it is contagious, fence line neighboring and comingled herds, as well as any herds that purchased cattle out of the infected herd, must be tested.
It is unclear how the infected herd contracted bovine TB in the first place, so in an effort to unravel the mystery, all herds that sold cattle into the infected herd will also be tested.
“At this point we have over 50 herds that we have some interest in,” Zaluski added.
Bovine TB is an extremely disruptive disease and owners of infected herds are left with limited options. The whole herd becomes quarantined and any with bovine TB must be dispatched. From there, depending on several different factors, the whole quarantined herd can undergo serial testing every few months to detect and remove positive animals. Known as testing-out, this process can take up to two years to complete and marketing options for the herd are essentially null until the entire herd tests clean. The other option is to depopulate all or some of the herd with the federal government offering a per head indemnity.
“It’s a really complicated process and it can be really frustrating for people. There are a lot of moving parts and you have got to have empathy for the operations involved in this investigation, particularly during this tough year with the drought,” Zaluski stated.
With it being fall and the time of year the majority of cattle are marketed and moved in Montana, MDOL officials are working as quickly as they can to test and release herds from the investigation. Zaluski is quick to tip his hat to all the producers, landowners, and officials whose efforts are what is making this epidemiological investigation possible.
In conclusion, Zaluski wants Montana producers to know the confirmation of a bovine TB-infected herd will not affect the state’s TB-fee status.