Hoary Alyssum Poisoning in Horses
Key takeaways
Hoary alyssum poisoning in horses is a rare and potentially life-threatening condition resulting from the ingestion of large quantities of hoary alyssum (Berteroa incana) plants.
- The specific toxin responsible for the poisoning is unknown
- Symptoms are seen when the amount of hoary alyssum ingested is more than 30% of the animal's total diet
- Symptoms include limb swelling, lameness, and potentially life-threatening laminitis
- Diagnosis is based on history of exposure, diagnostic imaging, urinalysis, and blood tests
- Treatment options are mostly of a supportive and symptomatic nature
- Prognosis depends on the amount of toxic plants ingested, timing of treatment, and the severity of laminitis
- Horses that do not receive proper medical attention or who have consumed a large amount of hoary alyssum may develop severe laminitis and often require euthanasia
- There is no antidote; prevention is the best way to ensure horses' well-being
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A closer look: Hoary Alyssum Poisoning in Horses
Hoary alyssum (Berteroa incana) is a biennial weed that grows throughout Canada and the northern United States. Hoary alyssum toxicosis is rare in horses but is potentially life-threatening, and as such, must be treated as an emergency.
Prompt treatment is crucial in ensuring that affected horses do not develop severe laminitis.
Due to the absence of an antidote, prevention is the best way to ensure the safety and well-being of at-risk horses.
Risk factors
Hoary alyssum ingestion can cause severe laminitis, an extremely painful condition of the hooves.
Symptoms of laminitis include:
- "Sawhorse" or "camped out" stance (front limbs extended forward and weight shifted backward)
- Warm hooves
- Refusal to move
- Lameness
- Recumbency
In severe cases, the bone within the foot may protrude through the sole of the hoof, or the hoof may completely slough from the body. Abortion can occur in late-term mares.
Possible causes
Toxicosis is caused by the ingestion of large quantities (over 30% of the diet) of hoary alyssum plants. It is toxic in both its green and dried forms.
Contaminated hay is a common cause of poisoning.
The specific toxin and poisoning mechanisms are currently unknown.
Main symptoms
Symptoms occur within 12 to 24 hours after ingestion of a toxic amount.
Testing and diagnosis
There is no specific diagnostic test for hoary alyssum poisoning, as the toxin is unknown. Horses presenting symptoms of hoary alyssum toxicosis undergo the following diagnostics:
- Physical examination
- Blood work
- Diagnostic imaging, including X-rays of the hooves
- Urinalysis
Testing and diagnosis
There is no antidote for hoary alyssum poisoning, and treatment is supportive and symptomatic. Treatment options include:
- Removal of toxin source
- IV fluid therapy
- Electrolytes
Laminitis treatment options include:
- Anti-inflammatories
- Pain medication
- Stall rest
- Cold- water therapy or icing the hooves
- Specialized shoeing or packing of the hooves
Horses diagnosed with laminitis require long-term monitoring.
Prognosis varies depending on the quantity of toxin ingested and the timing of treatment.
With prompt treatment and removal of the source of the toxin, most horses are able to recover within two to four days.
If medical attention is delayed, affected horses develop laminitis.
Horses diagnosed with mild laminitis are generally able to return to normal activity after rehabilitation.
Horses that develop moderate laminitis typically recover for pasture soundness but are rarely able to return to athletic activity.
Horses that develop severe lameness due to laminitis have a poor prognosis and are often euthanized.
Prevention
Hoary alyssum toxicosis is not contagious.
Horses that do not ingest Berteroa incana plants do not develop hoary alyssum poisoning. Prevention strategies include:
- Ensuring that hoary alyssum does not exceed 30% of the horse's diet
- Providing abundant alternative feed
- Inspecting pastures and hay prior to feeding
- Removal of hoary alyssum plants from pastures
- Buying high-quality feed from reliable sources
Removal of hoary alyssum plants from pastures is the best prevention method; however, caution must be taken as several herbicides can also be toxic. Herbicide instructions must be followed precisely.
Most horses prefer to graze on other plants, however in some cases this preferential grazing can cause hoary alyssum to ultimately be the most prevalent plant in the pasture.
Is Hoary Alyssum Poisoning in Horses common?
Hoary alyssum poisoning is a rare condition.
Horses with access to uncontaminated feed usually do not ingest hoary alyssum due to its unpleasant taste.
Typical Treatment
- Removal of toxin source
- Cold-water therapy
- NSAIDs
- IV fluid therapy
- Electrolytes
