Tuesday, November 25, 2008

Watch out for crown vetch...

A friend of mine (yes, another friend's trauma forms the basis of a blog entry) has a horse that is showing some subtle neurological symptoms, similar to stringhalt (click for text description or video). She did some research and learned that ingestion of toxic plants can produce such neurological symptoms. Crown vetch, or Coronilla varia L, is a common plant that is known to produce stringhalt-like movement in horses. I have seen crown vetch where I board Harvey where many of us hand-graze our horses around vetch. It's toxic to horses? Who knew???

Crown vetch is toxic to horses because of the presence of nitroglycosides. The stems, leaves, and seeds contain the most nitroglycosides. If consumed in large amounts, vetch can cause paralysis, weight loss, poor growth rates, depression, ataxia, staggering (hindquarters), heart irregularity (with consumption of the seeds), rapid respiratory rate, and difficult breathing. While the lethal amount of vetch is not known, consuming large quantities vetch can be fatal. Note that ruminants like cows can consume it with no ill effects; but single stomached animals like horses cannot.

Sounds pretty awful for anyone with a lot of vetch, doesn't it? It's one of those introduced species that got out of control -- like kudzu -- and it's hard to eradicate. When I contacted Rutgers University, veterinarian Dr. Carey Williams offered some good advice.

If you have crown vetch...

It's tough to get rid of, but there are herbicides for keeping it in check. You can also limit growth and reduce grazing activity by frequent mowing. Making sure horses have enough good grazing pasture will make it less likely they'll turn to vetch. Adding alfalfa to the horse's diet also helps reduce the effects of the toxins.

Hairy vetch is also toxic. Crown vetch may be confused with partridge pea (Cassia fasciculata) or other native vetches (Vicia sp.)


Poisonous trees and plants can be harmful to your horses

Toxic plants


  1. This sent me looking in my Texas wildflowers book. It listed Winter Vetch. It mentioned that it was introduced from Europe as a ground cover and can take over whole pastures. I think we are a little too far west for it. It probably likes more rain than we get. I've counted over 2 dozen different kinds of wild flowers on our little property, but I'm hoping this won't be one of them. Somehwere I have a book of plants that are toxic to horses. If I find it, I'll look in it. Thanks for the heads up.

  2. Thanks for the information. I've done some extensive research into plants that are toxic to horses and I don't have this one on my list yet.

    (The second resource link isn't working by the way).


  3. Oh my. I have some of that around my place. I don't think I have any in the pastures (I'm pretty neurotic about eradicating ALL WEEDS!), but still...that stuff could spread.

    Thanks for the warning.

  4. I am Dr. Carey Williams, and just wanted to clarify, I am not a veterinarian. I am the Equine Extension Specialist for Rutgers University, and I specialize in Nutrition and Exercise Physiology. Please visit our website for more questions and asnwers... http://www.esc.rutgers.edu/Q_A.htm.

    Thank you,
    Dr. Carey Williams


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