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"Poisonous" does not mean deadly. Some manifestations of toxicity are subtle. The dose, as always, determines if a plant is safe source of nutrients or a toxic hazard.

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BRIEF: Do you have any information on hoary allyssum?

We recently had a horse die, the vet said it was a poisonous plant. I believe its called "hoaryallysum", I don't have the correct spelling. We had some straw we baled up and put down for bedding, that's the only thing different. The other horses and mules didn't get sick. Would you know how much of this the horse would have had to eat? We need to know what it looks like so we can get rid of the straw bales that are bad. The horse that died from this had a very severe cough, it seemed similar to when a human has dry heaves. We are planning on plowing up the new seeding that had the straw on it, because we don't know what we are looking for in a weed or plant. If you could send me some information or someone to contact, I would be very grateful.


Although hoary allyssum is poisonous to horses, it is reported to cause a high fever, colic, and swelling of the limbs rather than a cough. This person may have misunderstood her veterinarian. The poisonous plant may well be on the farm but the horse might have died of allergic lung disease (heaves) from dust in the straw or from pneumonia. The straw bales may be bad because they are dusty. If you lack papers on hoary allyssum I can send copies to you campus mail.