Plants Toxic to Horses
I recently wrote an article, Simultaneous Ivermectin and Solanum plant Poisoning in Horses for The Horse, and it got me thinking about plants that are toxic to horses. I have to admit, it’s not something I’ve worried about too much, but it’s a real problem–and probably exacerbated by the drought conditions much of the country has experienced last couple of years. The drought has led to decreased hay supplies, forcing many horse owners to buy poorer-quality hay, perhaps. It’s also dried up pastures, and horses may be eating plants that they wouldn’t normally eat.
So what dangers could be lurking in your horse pasture? I’ve put together a list of some common plants toxic to horses:
This plant has fern-like leaves with clusters of small, white flowers. Often grows along roadsides, but can grow in other areas. The leaves, stems, and seeds contain neurotoxins that will adversely affect the horse’s central and peripheral nervous systems. Horses will likely avoid this plant. If a small dose is consumed, the animal may recover. A large dose (4-5 lbs) is lethal.
We’ve all likely seen this one. Course-stemmed grass that can grow up to six feet in height. Often grows along roadsides or uncultivated pasture-areas. The leaves and stems contain a cyanide compound. Young johnsongrass is more toxic than the mature plant. Horses can usually tolerate eating a bit of mature johnsongrass (I know mine have grabbed a bite while riding through fields of it), but stress caused but frost, drought, etc, can ‘free’ the cyanide within the stems and leaves, leaving them highly toxic, not just to horses, but to other grazing animals as well.
3. Red Maple Tree
This is a medium-sized tree that will have green leaves in the spring and summer, with the leaves turning red in the fall. Healthy leaves on the tree don’t seem to be harmful, but wilted red leaves (that have fallen) are toxic to horses. Eating a pound or two of these leaves can kill a horse.
4. Common Milkweed
This is a perennial plant that grows between 2 and 4 feet tall. It’s often found on roadsides, in wooded areas, or in pastures and has eliptical-shaped leaves and fragrant pink to reddish-purplish flowers. Horses are unlikely to eat common milkweek, but they might if they have no other food source. Toxic, but rarely fatal.
Flowering plant that grows 6 inches up to 2 feet tall. Yellow flowers with 5 petals. Common in meadows, pastures, and roadsides. Fresh flowers and leaves are toxic to horses, but the dried plant (in hay) is not toxic.
6. Oak Tree
Young leaves and acorns (especially when green) from the oak tree are the toxic. The tannic acid in the acorns can harm the horse’s intestinal lining. Can cause death if enough is consumed.
7. Field Horsetail
All parts of the field horsetail plant are poisonous to horses, whether they are fresh or dried (in hay). This light-green plant can be found in sandy-soiled, poorly-drained, or wooded areas, and along roadsides. It appears in early spring, with slender, jointed stems with a pinecone-like head. It does not produce flowers.
8. Bracken Fern
This entire fern is toxic to horses as well. It can be found in fields, wooded areas, and often grows in dry, rocky soil. Can grow 2-3 feet high and has triangular-shaped leaves. Contains the toxin, thiaminase and can cause neurological impairment in horses if consumed. It would take an extremely large amount of bracken fern kill a horse, but horses like the taste of this plant and will readily consume it.
These are just a few of the plants and trees that are poisonous to horses, but they are common in many areas of the country and might be in your pasture or paddock. Keep an eye out for them. If you suspect your horse has consumed a toxic plant, contact your vet immediately.