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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: Is alfalfa hay causing the welts on my horse?

I have a horse that is swelling and getting large welts all over his body. Our vet can not quite pinpoint the cause of this reaction. The varible that is constant when he reacts this way is when he is put on alfalfa hay. Could you please send me information on this area of study and how it can affect horses?


I think you are lucky that you have been able to associate the welts (urticaria, in med-speak) with one feed source, as usually we don't have a clue what in the horse's environment is triggering this allergic reaction. If good grass hay is available, the least expensive way to handle this horse would be to avoid feeding alfalfa to him. The antihistamines in horse-size doses are very expensive and the steroids on a daily basis to try to prevent an allergic reaction would be asking for other health problems to develop.