Onion toxicity

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Onion Toxicity

Onion Poisoning

Onions, garlic, leek, shallot and chive are from the Allium genus of plants, which are toxic to horses if ingested.
Wild garlic toxic horses
The plants contain propyl disulfide which can lead to the formation of oxygen free radicals that damage the membrane of red blood cells, causing cells to release haemoglobin.

The haemoglobin binds to the inside of the red blood cells and forms Heinz bodies. These damaged red blood cells are removed from circulation which causes the horse to become anemic; the specific condition is called Heinz hemolytic anemia.


Dark red-brown urine
Sulfur or onion odor breath
Pale mucous membranes
Increased heart rate
Abortion in mares


  • History
  • Clinical signs
  • Physical exam
  • Blood gas analysis



Removing onions from diet
Symptomatic and supportive treatment
Blood transfusion


  • 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.

Scientific Research

General Overviews

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Risk Factors

  • Allowing horses access to wild onions while in horse pastures
  • Feeding horses onions from table scraps, purposely or accidentally.

Also Consider