Equisetum hyemale toxicity

Recently I saw my horse (6 years old) digging in the snow and eating a particular weed. After research I found the name of a weed in my pasture... Equisetum hyemale (horsetails). I know that horsetails are toxic to horses.Recently I saw my horse (6 years old) digging in the snow and eating a particular weed. After research I found the name of a weed in my pasture... Equisetum hyemale (horsetails). I know that horsetails are toxic to horses.

Story originally posted by: Michael Lowder, DVM, MS

Dear Dr. Lowder,

Recently I saw my horse (6 years old) digging in the snow and eating a particular weed. After research I found the name of a weed in my pasture… Equisetum hyemale (horsetails). I know that horsetails are toxic to horses.

The book I own on toxic plants for horses did not show a picture of this weed (…thought I had done my homework).

My question is how toxic (amount required), how soon is the onset of symptoms and what are the symptoms? This happened about a week ago and so far seems fine.

Should I be doing anything immediately?

Sincerely,
L Young
Quebec, Canada

Hello,

There are two types of horsetail, E. Arvense and E. Hyemale, both can be found in the US. Both plants can be founded on the internet to compare picture.

E. Hymale is highly toxic to horses and feeding hay that contains horsetail can be toxic.

The fresh plants tends to be unpalatable and most toxicities due to plants mixed in feed signs of toxicity are weakness, hypersensitivity, increased irritability and inability to rise. Toxicity may also cause death.

Watch the horse for any changes in the attitude or appetite give thiamine by injection. For acute toxicity, 100-200mg thiamine SIDx1Wk and no more access to horsetail.

Thanks,
Dr. Lowder