Clover toxicity

Veterinary advice should be sought before applying any treatment or vaccine.

Clover Toxicity

Alsike Clover Poisoning

Clover toxicity is caused by consumption of alsike clover (Trifolium hybridum) or red clover (Trifolium pratense). There are two forms of toxicity associated with ingestion of these two species of clover---photosensitivity and liver failure. Both species of clover are found in pastures throughout North America and grow best in cool climates with heavy, poorly drained clay soils.

Alsike clover thrives in adverse weather conditions such as cold, drought and excess rain, which often causes it to become invasive, taking over the pasture and replacing the grass.

The majority of toxic cases occur between April and November. Horses need only to ingest as little as 5% of fresh pasture or contaminated hay to begin to develop signs of toxicity. Signs usually develop 2-4 weeks following ingestion. The potency of the toxin is increased if consumed with dew or under hot and humid conditions.


Weight loss
Loss of appetite
Oral lesions
Behavior changes


  • History
  • Clinical signs
  • Measure the serum enzyme activity of aspartate amino transferase (AST), gamma glutamyl transferase (GGT), sorbitol dehydrogenase (SDH) and lactic dehydrogenase - 5 (LDH-5)
  • Biopsy



Remove source from diet
Protect horse from direct sunlight
General therapy for photosensitization and liver failure


  • Make yourself aware of the weeds and plant species that can be invasive in pastures and/or poisonous to horses.
  • Take periodic walks around pastures to check for the presence of potentially poisonous plants
  • Check that hay does not contain dried up poisonous plants
  • If you borrow or hire farm machinery ensure it is clean prior to arriving on your property, the same goes for lending of your own equipment.
  • Quarantine new animals in a separate paddock the first 10 days to 2 weeks after arrival. Weed seeds can be passed through an animal's digestive tract.


Good if discovered early prior to any liver damage occuring.

Scientific Research

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