Chokecherry bushes had lethal levels of prunasin

Chokecherry bushes in the Northern Agricultural Research Center pasture where two local horses died last week contained a fatal level of a compound known to cause cyanide poisoning in livestock, the center's superintendent said Tuesday.

Gregg Carlson said lab results from Montana State University-Bozeman show that both samples of the chokecherry bushes taken from the pasture had levels of prunasin well above the amount considered potentially toxic. Prunasin releases cyanide when combined with water in the stomach of livestock.

Foliage containing between 600 and 1,800 parts per million of prunasin is considered potentially toxic, and more than that is considered very toxic, said Carlson. One of the samples had 2,500 parts per million and the other had 3,600 parts per million, he said.

Prunasin content in chokecherry foliage becomes more concentrated after a freeze like the one that hit the Havre area two weeks ago.

The bushes in the pasture had been browsed, but Carlson said it is not yet known whether the horses or some other animal ate them. The results of toxicology tests done on tissue samples from the dead horses should be complete in the next few days, he said.

After the horses, which were owned by research center employees, were found dead on May 10 in a pasture with plenty of food and water, officials speculated that chokecherry foliage, poisoned oats in the pasture, or a combination of the two may have contributed to the animals' deaths. The horses weren't supposed to be in the pasture, Carlson said.

He said the presence of chokecherry foliage is "not a new problem and it hasn't been known to be a widespread problem before in killing domestic livestock. We don't want people to panic at this point."

"I don't want to jump to any conclusions unless we know the facts," he added.