Rayless Goldenrod Toxicosis in Horses

Key takeaways

Rayless goldenrod toxicosis in horses is a life-threatening condition caused by the ingestion of a toxic dose of the Isocoma pluriflora plant, commonly referred to as rayless goldenrod.

  • When ingested, the toxin contained in the plant affects the muscle tissue, causing skeletal muscular degeneration
  • Symptoms include acetone-smelling breath, muscle tremors, paralysis, recumbency, difficulty breathing, and loss of consciousness
  • Diagnosis is based on a history of exposure, bloodwork, and tissue biopsy
  • Currently, there is no specific available treatment for rayless goldenrod toxicosis
  • Prognosis is dependent on the amount of toxin ingested and the timing of treatment
  • If the animal suffers respiratory system paralysis or severe cardiac irregularities, prognosis is extremely poor
  • Due to the absence of a specific treatment, prevention is of the utmost importance
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A closer look: Rayless Goldenrod Toxicosis in Horses

Rayless goldenrod toxicosis is very rare but potentially life-threatening and must be treated as an emergency. Horses not promptly treated can die within a few days from ingestion. The ingestion of 1 to 2% of the animal's body weight over the course of several weeks can cause fatal toxicosis.

Risk factors

Conditions such as drought may increase the risk of toxicosis, as fewer desirable forages or plants are available for consumption. Rayless goldenrod is commonly found in the southwestern United States (Arizona, New Mexico, and Texas) and northern Mexico.

Horses consuming rayless goldenrod may develop heart failure, due to degeneration of the heart muscle.

Possible causes

Rayless goldenrod toxicosis is caused by the ingestion of toxic amounts of the Isocoma pluriflora plant.

The toxin found within rayless goldenrod accumulates within the body, so ingestion over long periods can cause sufficient toxin accumulation to cause symptoms. Symptoms can also arise from eating a large amount of the plant in a short period.

Main symptoms

Testing and diagnosis

Diagnosis is based on symptoms and history of exposure. Horses presenting with symptoms of rayless goldenrod poisoning generally undergo the following diagnostics:

  • Bloodwork
  • Urine analysis
  • Examination of stomach contents
  • Muscle biopsy
  • Electrocardiogram

Steps to Recovery

Currently, there is no antidote or specific treatment for rayless goldenrod toxicosis. Treatment is of supportive and symptomatic nature. Treatment options include:

  • Prevention of further ingestion
  • Activated charcoal to reduce toxin absorption
  • IV fluid therapy

Note: Induction of vomiting or administration of activated charcoal should only be performed by a veterinarian. There is no safe way to induce vomiting or administer activated charcoal at home.

Prognosis of rayless goldenrod ranges from guarded to extremely poor depending on the amount of toxin ingested and the timing of treatment.

If treatment is delayed or the condition is left untreated, the prognosis is poor, with many horses dying within a few days from ingestion due to cardiac complications. Horses that survive often develop scarring of the heart and heart failure, and have a poor long-term prognosis.


Rayless goldenrod toxicosis is not contagious, but lactating mares can transmit the toxin through their milk.

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

  • Removal of rayless goldenrod plants from pastures
  • Feed analysis prior to feeding
  • Ensuring affected mares do not nurse foals

Is Rayless Goldenrod Toxicosis in Horses common?

Rayless goldenrod toxicosis is a rare condition.

Typical Treatment

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

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