Black Locust Poisoning in Horses

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Last updated on
4 min read

Key takeaways

Black locust poisoning is a potentially life-threatening condition in horses, resulting from the ingestion of the seeds, leaves, or inner bark of the black locust tree. 

  • Symptoms of black locust toxicosis generally present within two hours of ingestion and include abdominal pain, diarrhea, blood in feces, and dilated pupils
  • Diagnosis is based on symptoms, physical examination, and identification of black locust in feed or stomach contents
  • Treatment is of a symptomatic and supportive nature; options include activated charcoal, and IV fluid therapy
  • Due to limited treatment options, prevention is paramount
  • If medical attention is delayed and symptoms of toxicosis develop, most horses die within several days from ingestion
  • Horses treated shortly after ingestion can recover with no long-term effects
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A closer look: Black Locust Poisoning in Horses

The black locust tree is native to the Eastern United States, but populations are found in temperate climates all over the world. All parts of the tree, except its flowers, are toxic to horses.

Some horses with black locust toxicosis develop acute laminitis, painful inflammation of the tissues inside the hoof. Symptoms include:

  • “Sawhorse” stance with the weight shifted backwards with the front limbs extended forwards
  • Unwillingness to move
  • Lameness
  • Warm hoof capsules

Severely affected horses may become recumbent, and unable to rise.

Affected horses should be quarantined, as seeds can pass through the gastrointestinal tract producing toxic manure.

Risk factors

Black locust toxicosis is potentially life-threatening and must be treated as an emergency. The ingestion of as little as 0.04% of body weight can cause toxicosis. Horses that are not treated can die quickly, often within a few days of ingestion.

Ingestion of black locust is among the leading causes of plant toxicosis in horses, but is overall uncommon.

Horses that are hungry or bored are more likely to consume the plant, particularly since the leaves and bark of the plant are palatable.

Horses with access to adequate amounts of uncontaminated forage tend not to eat black locust.

Hosers diagnosed with pica are more likely to ingest black locust.

Possible causes

The ingestion of seeds, leaves, and the inner bark of the black locust tree (Robinia pseudoacacia) causes black locust toxicosis.

The black locust tree contains a number of toxic proteins that affect the gastrointestinal and nervous systems. All parts of the tree, with the exception of the flowers, contain toxins.

Main symptoms

Symptoms of black locust toxicosis present 1 to 2 hours after ingestion.

Testing and diagnosis

There is no specific test to determine black locust toxicosis. Diagnosis is based on symptoms and history of exposure. Horses presenting with symptoms of black locust poisoning generally undergo the following diagnostics:

  • Physical examination
  • Neurological examination
  • Bloodwork
  • Electrocardiogram
  • Identification of black locust in feed or stomach contents

Steps to Recovery

Currently, there is no antidote or specific treatment for black locust poisoning. Treatment is of supportive and symptomatic nature. Treatment options include:

  • Prevention of further ingestion
  • Activated charcoal
  • IV fluid therapy

Note: always consult a veterinarian before administering activated charcoal to horses.

Prognosis of black locust toxicosis ranges from guarded to poor and depends on the amount of toxin ingested and the timing of treatment.

If medical attention is sought shortly after ingestion, horses can recover over the course of a few weeks, with no long-term effects.

If treatment is delayed, or the horse shows symptoms of toxicosis, the prognosis is guarded, with many horses dying within a few days of ingestion.


Black locust toxicosis is not contagious. Affected horses can pass seeds through their feces, which may then be ingested by other horses.

Due to the lack of specific treatment options, prevention is of the utmost importance. Strategies include:

  • Removal of black locust trees from pastures
  • Feed analysis prior to feeding
  • Quarantine of affected and new horses for up to two weeks

Is Black Locust Poisoning in Horses common?

Black locust ingestion is among the most common causes of plant toxicosis in horses, however is uncommon overall.

Typical Treatment

  • Prevention of further ingestion
  • Activated charcoal
  • IV fluid therapy


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University of Kentucky's College of Agriculture, Food, and Environment - Writing for The Horse
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