MSU Extension

Ornamental Plants Toxic to Michigan Horses

Introduction

People tend to keep horses, unlike some livestock species, close to their homes. After all, one of the joys of horse ownership is the ability to look out the window and watch them graze. In keeping horses close to home, however, it is important to consider the potential dangers that may lurk in the yard. Cultivating toxic plants around paddocks where horses may reach through the fence to consume the green on the other side can result in very sick horses, or worse! Horses may also escape the pasture on occasion, and though they often stick to the “grass that is greener on the other side of the fence,” some ornamental plants commonly used to beautify our yards are toxic to horses. Likewise, wellmeaning neighbors or family members may throw clippings over the fence to the horses to give them a “treat,” with disastrous consequences. In addition, horses without appropriate access to traditional forage including hay or grass may consume plants they would otherwise avoid. This bulletin highlights potentially dangerous ornamental plants. This is by no means an exhaustive list but includes plants horses could contact in the yard. If you have questions regarding the toxicity of a specific plant, please visit the Web sites listed at the end of this bulletin, or contact your veterinarian.

The yew family

A common, inexpensive evergreen landscape shrub with flat, needle-like leaves approximately 1 inch long tapering to a blunt point. Red, berry-like fruit will also appear. This plant is extremely toxic to horses, with sudden death often the result of consumption of as little as 6 ounces of fresh yew. All members of the yew family should be considered highly toxic to horses.

Rhododendron or great laurel

The great laurel is an evergreen tree with alternating oblong leaves and clusters of rose, white or single-colored flowers 1 to 2 inches wide. Animals typically do not eat the plant but will if no other forage is available. The cardiac effects of the poisonous principal grayanotoxin may cause death, although it has rarely been reported in horses. Symptoms include salivation, colic, repeated swallowing and weakness, followed by coma and death.

Foxglove

Known for its showy, slender, purple, pink, red or white tubular flowers, Foxglove is extremely toxic. The flowers themselves resemble the fingers of a glove and are found on a long stalk above the leaves of the plant. Consumption of only a few hundredths of a percent of the animal’s body weight are required for a fatal reaction, so horses should not be allowed to graze this plant. Colic, pain, irregular heartbeat and frequent urination are possible symptoms prior to death.

Oleander

Although oleander is not a commonly found outdoor plant in Michigan, it is a fairly common houseplant that may be placed in outdoor containers. Oleander has large clusters of red, white or pink flowers and thick leaves. Highly toxic, oleander will cause death. Clippings should not be fed to horses or any other livestock. As few as 10 medium-sized leaves may kill an adult horse.

Hydrangea

A woody shrub 3 to 5 feet in height with white, pink or blue flowers in dense heads and long, broad, oval leaves. Cyanide poisoning may occur if horses are allowed free access to hydrangeas or their prunings. Coliclike symptoms and bloody diarrhea may result upon consumption, along with labored breathing, weakness, coma and death if toxic levels of cyanide are absorbed from the intestinal tract

Delphinium species, larkspur

Also known as poisonwood or staggerweed, larkspurs are perennial herbs from 1 to 6 feet tall. The flowers are produced on the stalk at equal spacing above deeply divided leaves and typically are blue or purple, although other colors also exist. The stalk is not particularly palatable, and as a result, horses tend to avoid the plant, although they may consume it if quality forage is lacking.

Lilly of the valley

Small lily plant, 6 to 10 inches in height, with small, white, fragrant, bell-shaped flowers. Commonly found in gardens as a ground cover. Leaves and flowers are potentially toxic, although sheep and cattle are particularly susceptible

Azalea

All parts of this showy flowering shrub are moderately toxic. Symptoms include abdominal pain, stomach pain, abnormal heart rate, convulsions, coma and possibly death. Animals should not be allowed to graze these plants.

Literature Cited

(yew) Poisonous Plants of Pennsylvania: http://cal.vet.upenn.edu/projects/poison/plants/ppyew.htm

(oleander) Toxic Plants of Texas; Integrated Management Strategies to Prevetn Livestock Losses. 2003. Texas Cooperative Extension.

(rhododendron) Burger, Sandra. 1996. Horse Owner's Guide to Toxic Plants. Breakthrough Publications Inc. Ossining, NY.

(azalea) http://www.vet.purdue.edu/depts/addl/toxic/plant10.htm

(hydrangea) Burger, Sandra. 1996. Horse Owner's Guide to Toxic Plants.

(larkspur) Burger Sandra. 1996. Horse Owner's Guide to Toxic Plants.

(foxglove) Burger Sandra. 1996. Horse Owner's Guide to Toxic Plants.