Unusual adverse reaction to the anthrax vaccine by some miniature horses and young foals has prompted a warning for owners to consider alternative measures.
The advice comes from the company that makes the vaccine and from the Western College of Veterinary Medicine after several horses died within 10 days of being vaccinated to prevent the disease.
Chris Clark, a clinician at the veterinary college, said he still strongly recommends vaccination, but in areas where anthrax risk is high, it might be better to move miniature and young horses out of the pasture.
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They should be fed preserved feed or hay and given water from a water bowl.
These measures should reduce the risk, he said.
At least nine miniature horses, including six from a single herd, died after vaccination during this summer’s outbreak in Saskatchewan.
A veterinary pathologist at the college, Bruce Wobeser, said it appears the animals “had some sort of immune reaction to something in the vaccine.”
He did necropsies on seven of the horses and found all had died of renal failure. They did not have anthrax.
The American company that supplies the vaccine throughout North America is investigating, along with the college and the Canadian Food Inspection Agency.
Joe Huff, president of the family-owned Colorado Serum Co. that has provided vaccines since 1923, said this has never happened before.
“This is something brand new to us,” he said. “In 50 years (of supplying anthrax vaccine) we’ve never had a situation like this.”
No one yet knows if there is something in the genetic makeup of miniature horses or if size itself was a factor.
Sandra Stephens, spokesperson for the inspection agency, said in all cases the injection site swelled more than usual and the horses became ill. The owners didn’t necessarily know something was wrong.
“You expect a certain amount of reaction to know it’s working,” she said of the vaccine.
Clark added that the number of adverse reactions, while difficult for the owners, is actually quite small, considering more than half a million doses were sold this summer.
The agency’s Sept. 8 update on Saskatchewan anthrax cases showed that 779 animals had died and 153 farms had tested positive. No new cases were reported in Manitoba.
Anthrax is a reportable disease. Asked if she was worried that some farmers aren’t reporting it, Stephens said it is possible that some aren’t or that animals are dying out in pastures and not being found.
In some cases, farmers who learned of positive tests telephoned all their neighbours to let them take preventive steps. In other cases, farmers didn’t want anyone to know.
But it’s important that the proper disposal steps be taken.
“The spores are there,” Stephens said. “We have no control or knowledge of where those spores are.”
Meanwhile, the federal government last week expanded the compensation available to producers who lose livestock to anthrax, retroactive to April 1. Producers can now receive compensation of $500 for disposal costs of bison, $350 for cervids and $100 for llamas and alpacas.
Cattle, horses, sheep, goats and swine were already covered.
