Tripp County herd under quarantine
The South Dakota Animal Industry Board confirmed Nov. 17, 2017, that bovine tuberculosis has been confirmed in a Tripp County, South Dakota, cattle herd.
The state veterinarian, Dustin Oedekoven, held a meeting with local producers Nov. 21, to help educate them about the disease and to answer questions.
The ranch remains under quarantine and because the state is handling the situation quickly and efficiently, the state’s TB-free status is not affected. This is the second confirmed TB case in the state this year — a Harding County herd was depopulated last April after testing confirmed infection in their herd.
“I think as long as we continue our investigation and response, there should be no reason to restrict movement of cattle out of South Dakota or to require additional testing (of cattle leaving the state),” Oedekoven said.
A cow from the infected herd went through Winner Livestock on Oct. 20, and was slaughtered in Texas on Oct 23, where the inspector discovered lesions during a routine inspection. The National Veterinary Services Laboratory in Aimes, Iowa, confirmed that the lesions were in fact the result of TB in that cow.
The ranch has since tested their entire cow herd, and about 30 percent of the mature cows and bulls tested positive for the disease using a test that does have a significant false positive response, Oedekoven said. The herd numbers less than 500 head, Oedekoven said.
“We do have a false positive rate with that screening test but it is designed to find those that we should look at further,” Oedekoven said.
A random group of 10 animals among those that tested positive were taken to the South Dakota State University laboratory for euthanization and testing, he said. The disease can’t be confirmed in a live animal — the animal must be put down so that tissue samples can be cultured in order to confirm the presence of the disease.
Six of the 10 were indeed infected with TB.
At that point, the state veterinarian’s office and state animal industry board confirmed that infection did exist within the herd, and together with the herd owner, discussion about future disease mitigation began.
The state veterinarian’s office has talked with all of the fence-line neighbors and all nine of them will be working with his office beginning to complete TB testing on their adult cattle that could have been exposed to the infected herd. At this point, the only herd under quarantine is the known infected herd.
“We’re learning as we go here,” Oedekoven said — referencing the Harding County case where all fenceline neighors were quarantined until testing showed that their cattle were not infected. “We’ll be essentially accomplishing the same task, and they’ll be able to continue marketing their calves,” he said.
State and federal health officials are also in the process of tracing out animals that have left the infected herd. “Those are a higher priority,” than neighboring cattle at this point, Oedekoven said.
Because the herd is a relatively closed herd — with basically just bulls being purchased in recent years, but not females — identifying the cattle that have been added to the herd is not a difficult undertaking.
The next step for the infected herd will be removal of the remainder of the animals that reacted to the first test, Oedekoven said.
Those animals will be slaughtered at a TB-approved plant where inspectors will determine which animals are infected and should be disposed of, and which are healthy and can go through the slaughter process.
The level of actual infection in those cows will help determine the next step. “We will determine the next route from there. Do we seek funds for whole herd depopulation or do we develop a ‘test and removal’ plan and try to test and remove?” Oedekoven said. If the herd is not depopulated, testing would continue for several years to determine infection because some cows have been exposed to the disease but have not yet developed a response.
“This is a herd of beautiful cattle,” Oedekoven said, explaining that making decisions in this kind of situation is never easy. “We develop a personal attachment to our cattle.”
The strain of TB in the original infected cow has common ancestry with a Mexican strain, Oedekoven said, and it is not the same strain as the Harding County herd had.
“The science to this leaves more questions than answers right now,” he said, adding that further research and testing will hopefully produce more answers as to how the disease was introduced into the herd. No cattle from Mexico have ever been added to the infected herd.
Oedekoven said any cattle that cross the border from Mexico into the United States must test negative for TB. Additionally, cattle that originated in Mexico — even if they’ve been in the United States for a while — are required to test negative again for TB within 60 days of importation into the state.
As a general rule, individuals who have cattle from Mexico should keep them separate from their domestic cattle.
The South Dakota Game, Fish and Parks department is working on a surveillance plan for area wildlife, Oedekoven said.
Tripp County is in the south central part of the state — along the Nebraska border and one county west of the Missouri River. ❖
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