Mycoplasma bovis more likely in large herds

Researchers found bison farms in Alberta were 22 times more likely to have the disease than those in other provinces

A study to determine the prevalence of mycoplasma bovis in bison has found two clusters in Alberta and on the Saskatchewan-Manitoba border over the past five years.

Researchers at the University of Saskatchewan and University of Calgary’s veterinary schools have been examining the disease, which has devastated individual bison herds, particularly in Alberta.

Ana Bras of the U of C said 467 producers were selected for a telephone survey in 2013 and 2014 to determine prevalence.

Of those, 33 in Manitoba, 71 in Saskatchewan, 75 in Alberta and 23 in British Columbia responded

“What we saw was that out of the 202 producers, 12 actually had a mycoplasma outbreak in the last five years,” Bras told the Canadian Bison Association’s annual conference in Regina last week.

These were lab confirmed positive tests between April 2009 and 2015.

“Operations located in Alberta were 22 times more likely to be affected than operations in other provinces,” Bras said.

As well, larger farms were more affected.

“For every 100 head increase in herd size, the odds of being an affected herd increased one-and-a-half times,” she said.

Increasing herd size is associated with the number of weaned calves, and operations bringing in calves were most affected, she added.

Work to determine clinical expression and risk factors for M. bovis was also done through a telephone interview and an Alberta mortality study.

Forty-nine participated in this part of the research: 17 had affected herds and 32 were unaffected.

Bras said the symptoms include lameness, reluctance to move, swollen joints, difficulty breathing, coughing, loss of body condition and reproductive problems. At least four symptoms must be present to be considered affected.

For example, she said poor body condition was present in all the affected herds but was also common in unaffected herds.

However, swollen joints were observed in 94 percent of affected herds versus just nine percent in the others, and breathing difficulties were seen in 82 percent versus six percent.

Bras said the survey found that clinical signs appeared one to 96 weeks after the first case was identified. Confirmation is obtained post-mortem.

The average was 12 weeks.

“Most of our affected herds actually introduced new animals before this first case was diagnosed,” she said. “These new animals were healthy when they arrived but later developed signs.”

She said it isn’t known whether they were already infected and the stress of moving encouraged the disease to progress or if they were infected during transportation.

“What we do know is that these new animals were introduced two to 32 weeks and an average eight weeks before diagnosis,” Bras said.

The study has also found that cows are more affected than yearlings, and the death rate is high.

Producers have tried antibiotics, isolation and keeping closed herds, but those measures are perceived to be ineffective. The disease has recurred in 11 of 17 herds, sometimes up to four years after the first outbreak.

Stress, transport, mixing and biosecurity are considered the main risk factors. Feedlots are seven times more likely to be affected.

Bras also said producers who regularly rent trailers or use trailers from other farms are 15 times more likely to see the disease occur.

“There are studies that show that mycoplasma can survive in manure, in straw, in steel for many days,” Bras said.

“If these trailers were not well cleaned, that could be an issue.”

The research has also found that affected herds were seven times more likely to be vaccinated, but Dr. Murray Woodbury of the U of S’s Western College of Veterinary Medicine said that’s likely because of animals being into herds.

As well, Woodbury said cattle vaccines don’t work well in bison and no bison vaccine trials are underway.

Biosecurity measures and close monitoring of bison herds are the best control methods, Bras said.


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