Lupinus species

Lupine, which is poisonous to horses.

Credit: U.S. Fish and Wildlife Service

Plant Description

Lupines (also sometimes known as bluebonnets) are a group of plants that contains both annual and perennial species. Some species are poisonous while others are not. However, like locoweed, it is hard for even experts to distinguish between some species so it is safer to simply assume that all species are toxic.

They are a part of the legume family, and have flowers that are 5-petaled. The flowers are usually some shade of blue or purple, but can be white, red, or yellow as well.

The seeds of this plant are small cream colored irregular circles, and are contained within a pod that is about an inch long.

Geographic Locations

This plant can be found throughout the United States, usually in cultivated gardens and landscapes in the east, but native in the south and west.

It prefers dry open areas and wooded areas, making it common in pastures as well as along forest trails.

Toxic Plant Components

This plant varies in its toxicity, depending on growing conditions and time of year. At some times of the year under certain range conditions, it is even safe enough to be used as a forage.

Lupinine, an alkaloid, is the offending substance in the plant, and can be concentrated in the seeds, making them the most dangerous. The pods can also contain high levels of the toxin. Lupinine is also found in the leaves and fruits.

The plant also retains the toxin when dried, which can cause problems if it is baled into hay.

Toxicity Cause and Symptoms

Since these species stay green after most other plants (and are palatable) and the pods are often high enough to be the last plant to be covered by snow, most poisonings occur in the fall and winter months, when animals are moved through infested areas, or infested hay is fed.

When a horse gains access to lupine just once, he will usually recover after being removed from access, if he did not consume large quantities.

However, when horses are exposed continuously to this plant, such as when fed infested hay, it can cause toxic hepatitis to develop.

Lupinine in large doses causes nicotinic reactions in horses, so symptoms will include:

  • Gastrointestinal problems, including diarrhea
  • Labored breathing
  • Reluctance to move
  • Changes in gait
  • Muscle spasms/loss of muscle control
  • General agitation and/or excitement
  • Coma

Cure and Treatment

The only cure and treatment for lupine poisoning in horses is to remove the animal from access to the plant and treat symptoms as the horse displays them.

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