Respiratory disease has emerged as a significant cause of death in Alberta bison herds.
“In my opinion, it’s the biggest single most significant disease affecting the North American bison industry,” said Dr. Roy Lewis, a veterinarian in Clyde, Alta., who is part of a team conducting autopsies on bison to identify causes of death.
He told the Canadian Bison Association’s annual convention in Regina Nov. 20 that mycoplasma bovis was the killer in half of the study animals younger than 30 months and almost all of those older than 30 months.
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He described the pathogen as being between a bacterium and a virus. It doesn’t respond to antibiotics and grows slowly and insidiously.
Autopsies show a condition similar to tuberculosis, with lesions in the lungs, that has developed for a long time. It compromises the animal’s immune system once it enters the lower respiratory tract.
Producers will notice bison weight loss, heavy breathing, coughing, lameness and abortions.
The disease is chronic and sometimes isn’t noticed until it is too late, Lewis said. Some animals may have had it without the producer’s knowledge.
An outbreak in Saskatchewan 10 years ago resulted in 18 percent death loss, but the following year it was gone.
A similar situation occurred in Kansas in 2004.
Lewis said there were outbreaks in three of Ted Turner’s herds in the United States in 1999, 2003 and this year.
In each case, the disease was there one year and gone the next.
He also said that Turner’s herds are isolated and closed. No herd bulls have been brought in for at least 10 years.
A research team comprising representation from Turner’s operations and the universities of Calgary and Saskatchewan’s veterinary faculties will study the disease further.
“Is it on the increase? I don’t know,” Lewis said.
However, at least nine or 10 Alberta herds were affected in 2010-11, and there is a possible outbreak in Oklahoma.
It’s possible that producers may need to keep new animals in quarantine for longer than they have been.
Lewis described outbreaks that occurred after new animals were introduced, but there were also cases in closed herds.
In one example, two groups of 30 cows and 50 cows were put together. There were 22 abortions and 13 dead cows, but only from the group of 50.
He and others have many questions.
Is there limited exposure to a mild carrier that prevents some bison from being infected? Is stress the problem? Would vaccination work? Why does it not reoccur?
Animals placed in feedlots seem to be under more threat because of the stress and commingling.
Researchers will be typing the m. bovis pathogen to determine which strain it is and whether a new strain is at work.
Lewis said the disease’s appearance is unfortunate, considering bison producers worked hard to con-t rol trauma and parasites and improve nutrition in their herds.
“Most of us were at the stage where everything was moving along ticketyboo,” he said.
Dr. Murray Woodbury of the Western College of Veterinary Medicine at the U of S said commercial vaccines don’t appear to help, but if producers want to try them they should make sure to use a killed product.
“With modified live virus vaccines, we actually knock those bison back,” he said, which gives pathogens such as m. bovis the opportunity to move in and take advantage.
Producers who plan to process their animals anyway and vaccinate against IBR with a killed product might be preventing m. bovis by doing so, Woodbury added.
