Tuesdays with Tony

Poisonous Plants

Plants are delicious. Who doesn’t love to chow down on a plant the humans have carefully placed for decorative purposes? I know I do. I have learned, however, that not all plants are safe for eating. This rule applies to cats, dogs, and horses.  This week I’m going to educate you humans on the top 5 poisonous plants in the horse world.

Quick dog and cat tip before I begin: Easter lilies are deadly to cats in very, very small amounts, and Coonti palms work the same way for dogs.

Red Maple

While beautiful, Red Maple trees are very, very bad for horses. Eating as little as 2 pounds of Red Maple leaves will cause toxicity in horses. Like many plants, wilted leaves contain the most toxin. The toxin, gallic acid, causes the body to attack and kill the red blood cells. This makes the blood unable to carry oxygen. Horses are affected within about 24 hours of eating. They become extremely depressed, and may even have blue mucous membranes. They will also urinate red or dark brown urine. There aren’t great treatment options for this toxin. The Docs give them lots, and lots, and I mean lots, of IV fluids. If they make it 36 hours, it’s very likely they will recover.

Since poisonous plants pretty much all look alike to me, I have included a pictures of these various plants.

Creeping Indigo

This is one horrible poisonous plant, and ‘Creeping’ is the key word. It creeps along very close to the ground, making it really hard to find. Creeping Indigo also spreads by long, hard-to-pull roots and seeds making it difficult to fully kill in one round. This plant makes you go to full-on war.  Horses need to eat around 10 pounds of creeping indigo daily for about 14 days to develop signs. That seems like a lot, but some horses develop a taste for this weed and seek it out! The toxins are 3-nitropropionic acid (3-NPA) and indospicine. These toxins attack the nervous system in many weird ways. That means the symptoms of Creeping Indigo toxicity are difficult at best to figure out. They can vary from runny, squinting eyes, sleepiness, nystagmus (this is the fancy term for eyes wiggling back and forth), gait abnormalities, and mild colic-type signs. Yep, a wide variety. To add to the joy that is Creeping Indigo, there are no lab tests to identify the toxin, and no real way to know if it’s the cause of the problem. Special tests on tissue taken after an animal has passed away can identify the toxin.

Here’s a picture of Creeping Indigo to help you identify it, with chapstick container for size reference. It will die if you spray it with Grazon, or other similar products, but you MUST pull up the dead plants since the seeds are still viable! The ways to hate Creeping Indigo are many.


Crotalaria is commonly known as rattlepods or rattlebox, due to the sound of the seeds rattling in their pods. This one suckers you in with pretty flowers, then BAM! Your liver gets annihilated. This plant really starts growing in late summer. It like damp places, such as the area around the water buckets or troughs in your pasture.

It has big broad leaves with a spike of small yellow flowers, and commonly grows to 4′ in height. Luckily, crotalaria tastes very bitter, so unless animals are starving, they usually won’t eat it. Interestingly, some less-toxic strains of this plant are consumed by humans in various places around the world. It just proves my point that some people will eat anything.

This one will happily die with pretty much any plant killer, but it does like to come back every Fall.   


This plant often gets planted as a decorative hedge. Horses think decorative hedges have been placed for snacking purposes. One mouthful of this hedge is enough to cause problems! In humans, a very small amount is enough to kill. The toxins in oleander are powerful cardiac poisons like digitoxigenin, and oleandrin. They target the heart muscle and cause it to die. Horses that eat oleander can show signs from poor performance to extreme lethargy depending on how much they ate. All I have to say about this one is don’t plant it in first place. If you do have oleander, be very, very careful removing it. All it takes is some sap in a small skin wound to cause problems with human hearts! 


Last of the horrible Top 5 poisonous plants is nightshade. This fun little guy loves to grow along fence lines. Long ago, crazy humans used the plant to dilate their eyes since they thought it looked good. The main toxin in nightshade is atropine. My Docs use it as a drug in its purified form. If your horse eats nightshade they will experience fun things like diarrhea, nervousness, irregular heartbeat, and extreme sensitivity to light. Luckily this guy also doesn’t taste very good. Keeping plenty of hay in front of your horses is a great way to keep them from checking out nightshade to see if it’s tasty. Most of the time this one can be treated with time. The easiest way to get rid of it is to check your fence lines regularly and simply pull them up. 

Poisonous plants are no joking matter. The best way to know what you’ve got? Call your County Extension Service and have them come walk your property. County Extension Agents are full of all kinds of useful knowledge about plants and grass. Best of all, they are part of your tax dollars at work!

Tuesdays with Tony is the official blog of Tony the Clinic Cat at Springhill Equine Veterinary Clinic in Newberry, Florida. If you liked this blog, please subscribe below, and share it with your friends on social media! For more information, please call us at (352) 472-1620, visit our website at SpringhillEquine.com, or follow us on Facebook!

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