Alsike Clover Poisoning in Horses

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5 min read

Key takeaways

Alsike clover toxicosis is a potentially life-threatening condition caused in horses by the ingestion of the Alsike clover (Trifolium hybridum). 

  • Ingestion of Trifolium hybridum can cause two syndromes: liver failure and dew poisoning (Photosensitivity)
  • Symptoms include yellow skin and gums, abdominal pain, sensitivity to sunlight, swelling of the skin, and skin sloughing
  • There is no specific antidote or diagnostic test for alsike clover toxicosis
  • Diagnosis is based on symptoms, history of exposure, and blood tests
  • Treatment options are primarily supportive
  • Removing access to alsike clover infested fields is a necessary treatment and prevention step
  • Prognosis is dependent on the kind of syndrome induced
  • Photosensitivity generally carries a good prognosis, while in the case of liver failure, it varies from guarded to poor and depends on the extent of liver damage
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A closer look: Alsike Clover Poisoning in Horses

Alsike clover is found worldwide in temperate regions. It has been widely cultivated for use in hay and silage.

Ingestion of alsike clover can cause two conditions in horses: liver failure and dew poisoning.

Liver failure: Depending on the amount of alsike clover ingested, liver damage associated with alsike ingestion can either occur suddenly or over a long period of time.

Dew poisoning (Alsike photosensitivity): Photosensitization primarily affects the white portions of the horse, such as markings or pinto patterning. Symptoms include

  • Red skin after exposure to sunlight
  • Swollen skin
  • Sloughing of the skin
  • Skin discharge
  • Excessive tearing

Risk factors

Alsike clover toxicosis is uncommon in horses. A wide variety of clovers can be found in horse pastures. Most clovers are a safe nutrition source, and have a high protein content.

Trifolium hybridum, commonly known as alsike clover, can be found in feed. When ingested in high quantities (20% of the diet), it can cause two syndromes: photosensitivity and liver failure.

Photosensitivity caused by alsike clover ingestion is not an emergency, and most animals recover rapidly once they stop consuming the clover. Due to skin damage from the condition, prompt veterinary evaluation is recommended for managing skin wounds.

Liver disease caused by alsike clover ingestion is a life-threatening condition and must be treated as an emergency.

The toxicosis is more common in wet and humid weather, coinciding with spring and autumn.

Possible causes

Alsike clover toxicosis is caused by ingestion of the alsike clover (Trifolium hybridum). Toxicosis occurs when 20% or more of the animal's diet consists of alsike clover.

The precise mechanism of the toxicosis is unknown, but the prevalence of poisoning during wet and humid weather seems to suggest the presence of fungal toxins. Ingestion of large amounts of alsike clover primarily affects the liver, leading to cell death.

Main symptoms

Testing and diagnosis

There is no specific diagnostic test for alsike clover-related syndromes, as the toxin is unknown. Horses presenting symptoms of alsike clover toxicosis generally undergo the following diagnostics:

  • Physical examination
  • Blood tests
  • Ultrasound of the liver
  • Liver biopsy

Steps to Recovery

There is no antidote for alsike clover toxicosis, and treatment is supportive and symptomatic. Treatment options include:

  • Removing horses from alsike pastures
  • Topical treatment of skin lesions
  • Keeping the animal out of direct sunlight
  • IV fluid therapy
  • Sedation if neurologic symptoms such as head pressing or ataxia are present

Prognosis of alsike clover toxicosis depends on the type of syndrome developed, and the amount of alsike clover ingested.

Horses suffering from photosensitivity generally have a good prognosis, and recover rapidly once removed from alsike clover-infested pasture. If the dermatitis is severe, the animal requires supportive care.

The prognosis for horses suffering from liver failure depends on the severity of liver damage, with many horses having a poor prognosis.


Alsike clover toxicosis is not contagious. Horses that do not ingest alsike clover never develop toxicosis. Prevention strategies include:

  • Ensuring that alsike clover does not exceed 20% of the animal's diet
  • Increasing the amount of clover-free feed or providing only clover-free feed
  • Reducing the amount of clover in pastures

Is Alsike Clover Poisoning in Horses common?

Alsike clover toxicosis is uncommon in horses.

Typical Treatment

  • Supportive care
  • Symptomatic care
  • Management changes
  • Keeping the animal away from direct sunlight


Jonathan H. Foreman , DVM, DACVIM - Writing for MSD Veterinary Manual
Anthony Knight, BVSc, MS, Dipl. ACVIM - Writing for The Horse
Alexander Campbell, BSc(Hons); Wilson Rumbeiha, BVM PhD DipABT DipABVT; Vetstream Ltd - Writing for Vetlexicon
University of Kentucky College of Agriculture, Food and Environment - Writing for The Horse
No Author - Writing for Veterian Key
No Author - Writing for Colorado State University College of Veterinary Medicine and Biomedical Sciences
No Author - Writing for Clinical Veterinary Advisor

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