Many people are not aware of the dangers of black walnut to equines. There are some permanent and deadly consequences that can arise just from coming in contact with them in shavings. Always know where your shavings come from. The best way to avoid getting black walnut in your shavings is to use a reputable shavings dealer or bagged shavings. DO NOT use shavings from cabinet companies or places that offer free shavings unless you are positive they do not contain black walnut. Pine shavings are the safest and most readily available supply. They are completely safe and non-toxic.
Black Walnut trees can be found from southern Ontario, west to southeast South Dakota, south to Georgia, northern Florida and southwest to central Texas. Familiarize yourself with the tree, because not only are the shavings toxic but having the trees in turnout areas are also very dangerous.
Some of the symptoms that could indicate a possible exposure are varying depending on the horse. Shavings with as little as 20% black walnut can be toxic to horses. Most of the cases are from horses ingesting the shavings, but can also be toxic through skin exposure. Horses may show signs of stiffness, swollen legs, depression, tender feet, laminitis and even founder. As the toxicity progresses there can be swelling in the neck and chest and also colic. Horses will usually have labored breathing with flared nostrils, increased heart rate and respiration. Mares have also been known to abort babies due to exposure.
Most horses in the mild stages recover quickly and on their own when the black walnut shavings are removed. But in more severe cases a vet needs to be called to treat the symptomatic factors associated with the exposure. If caught quick most horses recover with little to no long lasting effects. Treatment and removal as soon as possible is your best bet to a full recovery.
Please double check your supplier, and check your pastures for possible black walnut trees. This small step could save your horses life.
Here is an image search link. It shows what the tree, leaf and nuts look like.
Hope this was informative!