This week, as Dr. King was working on landscaping at the clinic, there was a lot of discussion about plants that can make us animals sick. Many times horses don’t eat toxic plants, until there is no choice between these plants and not eating; however, I decided it was worth talking about some of the most important plant species that can affect horses.  The best prevention for toxicity from wild-growing plants is to know how to identify them, and walk your pasture on a regular basis to identify and remove them.  Major trees/plants to be aware of include yew, red maple, cherry, oak, and ornamental flowers. These should never be planted where your horse (or other animals) can access them.

Florida or Japanese yew can kill your horse quietly in a matter of minutes – it is common to find the dead animal next to the yew. Animals will show nervousness, trembling, ataxia, and collapse will occur as the poison slows the heart to a stop.  Only 6 to 8 oz. will kill a large animal, and all species are susceptible to poisonings (including you people!). Do not plant this anywhere your animals may gain access to, or in a place where clippings may be thrown over the fence to your animals.


Red Maple

Red maple ingestion causes hemoglobin, the molecule in red blood cells that carries oxygen to the body, to change into methemoglobin, a less efficient form, for reasons unknown. This also results in rupture of the red cells, called hemolytic anemia. This effect is specific to horses. Wilted or dried leaves are the most dangerous (the toxin concentrates as leaves get ready for autumn). Fresh leaves do not appear to cause a problem. Signs of toxicity include dehydration, depression, and change in gum color (blue to brown, also yellow or “icteric”).  Increases in heart rate and respiratory rate are mild, but the urine will become dark red to brown. Death generally occurs 1-5 days following ingestion of a lethal dose.

Black, wild, and laurel cherry trees contain cyanide, which turns the horses’ gums red. This is a result of a decline in oxygen utilization.  Symptoms usually onset 30 minutes to an hour of ingestion.  The most toxic parts of the plant are the leaves and the seeds. One laurelcherry berry can kill a horse, and all animals are susceptible to cyanide toxicity.  There are many other species of plants that produce cyanide compounds, including elderberry, heavenly bamboo, hydrangeas, and various clovers.

Laurelcherry flowers

Oak leaves and acorns contain tannins, the substance that makes the Santa Fe River red.  The redder the leaf, the higher the tannins. Tannins cause kidney damage, making it difficult to form urine and regulate water and electrolytes. Clinical signs include colic, depression, frequent or no urination, constipation and/or bloody diarrhea.  “Oak bud poisoning” occurs when weather damages most available forages, and the budding oaks and acorns are most of what’s left.  In 1985, oak bud poisoning killed over 1,000 cattle in Sacramento, CA when snowfall left nothing but oak leaves to eat. Cattle and sheep seem most susceptible, while horses, goats and chickens are occasionally affected. Pigs seem to be resistant. All species of oak should be considered dangerous.

If it is an ornamental plant, has waxy leaves, seed “pods” of some kind, or berries, it probably isn’t something your horse should be eating. Most notable pods to stay away from include Crotalaria species, a yellow-flowered plant commonly referred to as “rattlebox.”  Ingestion of rattlebox can result in liver failure in the horse. Common signs with chronic toxicity are icterus, and signs of forebrain disease such as a change in attitude with depression, circling, and head pressing.


Another dangerous plant tip… don’t ever use black walnut shavings for your horses’ bedding.  It will result in laminitis with even limited exposure.

Thanks for visiting my counter, may your litterbox be clean and food bowl full!


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