Thiaminase containing plants


  • Source: Bracken fern (Pteridium aquilinum) and horsetail (Equisetum arvense)

Thiaminase containing plants

Toxic principles

  • Several toxic principles are recognized including
    • Thiaminase.
    • A factor that damages the bone marrow.
    • Ptaquiloside is the suspected carcinogen in brackenfern.
    • Cyanogenic glycoside (significance not clearly established).


  • Toxicity in horses (and rats) is due to a thiaminase enzyme which destroys thiamine in the digestive tract before it can be absorbed), resulting in central nervous system dysfunction and damage.
  • Thiamine deficiency results in impaired pyruvate utilization. Blood pyruvate levels rise. Animal suffers from abnormal energy metabolism due to inadequate ATP production.
  • Toxicity in cattle is due to an unidentified toxic principle and not thiaminase. At least part of the problem is due to a carcinogen.

Species affected

  • Cattle most commonly affected. Reports of poisoning in horses, swine, and sheep are less frequent.
    • Horses - Mainly neurologic.
    • Cattle - Mainly bone marrow damage.
Last modified: Thursday, 22 December 2011, 11:45 AM