I was originally going to include this in my Pets and Houseplants post, but there is just SO much to learn about toxic plants that this deserves its own feature. I was on a trail ride a few weeks back, and my gelding Rocky was trying to munch on some tree leaves that we were passing by. I told him, “No, Rocky, that’s a maple tree. It can be toxic to you.” Then a little farther down the trail, he went after an oak tree, and I told him the same thing. We also kept passing a bunch of flowering plants that I identified as White Snakeroot. By the end of the trail ride, my mother riding on her horse behind me asked if there was anything NOT toxic to horses! I assured her there are plenty of safe plants for horses, but I then realized how important it is to recognize the NOT safe plants. Here is just a shortlist of some toxic plants every horse owner should know.
- Red Maple. This is one of the plants I encountered on my poisonous trail ride. Luckily, red maple is usually only toxic when the tree leaves have turned red for Fall or when a branch has come off the tree and the leaves on it have wilted. Red maples produce a toxic agent most likely to be Hypoglycin A. This causes severe hemolytic anemia in the horse, and unfortunately horses that ingest too much Red Maple often die. It’s important to monitor for these falling leaves in the Fall and to make sure to pick up fallen branches in your horse pasture after a storm. These trees can be easily identified by their distinctive leaves.
- Black Walnut. This is a type of tree that can be found in North America. It has a distinctive knobby, dark-colored bark. This toxicity causes laminitis from the ingestion of the plant. The most common route of exposure is in wood chips for bedding. You should always check these for dark pieces instead of the usual light-colored bark. If there are dark pieces of wood chips, you should be very cautious about using this. Stalled horses will often drop hay or grain on the floor of their stall and then accidentally ingest some of the shavings while eating. If there happens to be black walnut they can get very sick.
- White Snakeroot. This is a small branching plant that has white flowers in late summer/early fall and likes to grow on the edge of tree lines. It has easy to recognize leaves that grow opposite one another. The toxin in white snakeroot is tremetol, which can cause a range of effects in both horses and ruminant species. In horses, it typically causes heart failure, and ruminants often have both heart and liver failure. It is important to monitor for this plant’s presence in your pastures.
- Oak. Oak is less likely to cause disease in horses, but it is still a really common plant that you should be aware of. The toxic parts of the plant are young, growing stems, and acorns. Acorns make this tree easy to identify. In horses, intoxication usually involves GI disease like colic, but it routinely causes kidney failure in ruminants.
- Johnson Grass. This is a type of grass that can be toxic to horses and ruminants. In drought or stressful conditions, it can produce dangerous compounds that basically cause cyanide poisoning. Cyanide binds to hemoglobin and prevents oxygen from reaching important organs. It is important to identify this plant and prevent your animals from eating it.
There are many other toxic range plants that horse owners should be aware of, but these are some of the important ones that I have learned so far in this semester in toxicology. It’s important to keep our animals safe and to keep pastures clean to prevent these plants from growing.