Toxic blister beetles kill 16 horses on Wisconsin farm

Published: Jan. 23, 2020 at 8:02 PM CST
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Blister beetles. They are not something South Dakotans have ever talked much about, dealt with or feared.

But the recent headlines out of a Wisconsin horse farm that hay - bought at an auction in South Dakota - contributed to deaths now of 16 horses, the latest to go down this morning, ha many asking what they need to know about the insect.

"We think of blister beetles being further south, not Wisconsin, not South Dakota. Yes, we've read that we do have them here," said Dr. Michelle Jensen, owner, and veterinarian with Dakota Large Animal Clinic in Harrisburg, South Dakota. "But, in 20 years of being a vet and working primarily on horses, I've never seen a case. So it can't be really common. But the necropsy reports were pretty convincing."

Dr. Jensen is looking at a couple of horses this day, but for something entirely different.

Blister beetle, she says, is not something she's ever felt the need to watch for.

In fact, she can list a host of other respiratory problems she typically sees, from moldy hay, in particular.

But perhaps this past year, with all of the flooding and hay in some places put up late, led to conditions perfect for the beetle to get into more of our fields.

They are bugs that follow the blooms.

And even a small amount of the bug itself or cantharidin, the toxic chemical it contains, experts say can be toxic enough to kill a horse within 72 hours.

"It can cause damage to the GI, mouth, esophagus, stomach, and kidneys, it's a very toxic substance," said Jensen.

That's what equine specialists say happened to at least 15 of the Wisconsin horses at Red Ridge Ranch Riding Stable in Mauston.

The horses, the owners tell us, had what looked like blisters and holes down their esophagus and throughout their insides.

Necropsy reports are being done on each of the horses to confirm their cause of death and the entomologist at the University of Wisconsin, they say, have also confirmed the presence of the beetle in their hay.

Cindy Kanarowski-Peterson tells me she has 15 more showing signs of distress.

The hay she had been feeding the herd, she says was purchased in four separate semi-loads over the course of several months from an auction site in Belle Fourche.

Dr. Jensen and others, including State Veterinarian Dustin Oedekoven, say while they look for more answers, and reiterate most of South Dakota's hay and alfalfa is safe to feed, it's best everyone right now know what the beetles look like, and what to watch for.

"I don't think we have a huge problem with them in South Dakota, it may have been just the right circumstance," Jensen said, of the hay from an auction in our state.

The Wisconsin horses, that we know, are the only ones to die as a result of the beetle this season.

Oedekoven says at this point, where the hay came from has not been pinpointed.

But to avoid the problem in the future, hay producers should always walk their fields before cutting, and avoid harvesting where they are present.

Horse owners in the meantime, should do all they can to buy from a local source, and buy the first cutting whenever possible. Because South Dakota typically has only one cutting, that may be why, according to Oedekoven, we don't see many problems with the beetle here.