I got started on poisonous plants last week and couldn’t get the doctors to stop so this week I am going to cover a few more, concentrating more on weeds than decorative plants.  A couple of items I learned from the docs this week:  most poisonous weeds like fence lines because they don’t get mowed there, low soil pH can promote weed growth and most horses will only eat poisonous plants if there is nothing else available or it is baled in to hay.

Deadly Nightshade

This is a very common plant seen on fence lines.  A very small amount of nightshade can be deadly!  Nightshade acts on a very specific portion of the nervous system leading to colic-like symptoms, dilated pupils, disorientation and loss of muscle control.  Keeping fence lines sprayed with herbicides on a regular basis or manual removal are the only ways to control this weed.  Don’t forget to check pastures occasionally, especially around trees, for additional plants.  Treatment is a drug called physostigmine or pilocarpine.

Bracken Fern

These ferns are commonly seen in wooded areas.  The most common way horses eat these ferns is if they are turned out in damp wood areas with limited roughage.  Symptoms are usually slow to present with the most common sign being weight loss.  Other symptoms include a decreased appetite, in-coordination and a characteristic wide leg, arched back stance.  The toxic portion of bracken fern causes a Vitamin B1 deficiency.  Treatment with Vitamin B1 is very effective if signs are caught early.


Many plants we use to attract butterflies are also poisonous to our horses.  Lantana is one of these.  Just like many other poisonous plants, horses will avoid them if given enough roughage.  Here at the office we keep our butterfly attracting plants outside the fence or away from horse areas to minimize risk of ingestion.  Lantana will grow wild in fields and along driveways and fence lines.  Horses do have to eat a large volume of lantana to cause toxicity.  Symptoms of large volume ingestion begin with photosensitization (sunburn on white markings), decrease appetite followed by yellowing of the skin and colic symptoms.  If horses eat small amounts over prolonged periods symptoms may begin with a bloody diarrhea, listlessness, colic symptoms and sores on the gums and tongue.  Treatment is only supportive, such as fluids, and often unsuccessful.


Milkweed is another common butterfly garden plant.  Unlike lantana, milkweed usually doesn’t grow well as a wild plant.  However, it can escape from gardens to grow in protected areas such as against barn walls, pump houses or the like.  Also unlike lantana, very small quantities can cause toxic signs with 1 pound capable of causing severe symptoms in a 1000 pound horse.  Symptoms include profuse salivation, colic symptoms and seizures.  Treatment can only be started within a few hours after eating and is often unsuccessful.  Prevention is the best treatment for milkweed.  Milkweed is also very poisonous to other pets like dogs and cats so be very careful with this plant!!

Many horses are naturally curious.  Unfortunately much like your 2 year old child, they explore with their mouths!!  Frequently walking your pastures on the lookout for poisonous plants is key to control.  Look for a seminar on poisonous plants in 2012 from Springhill Equine.  It will be held at the office so even us office cats can learn all about what plants to avoid.

Thanks for visiting my counter!  May your litterbox be clean and your food bowl full.  Tony