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What is Wild Onion Poisoning ?

Wild onion can be found growing in many regions where the climate is considered moist.  If ingested in large amounts by your horse, it can cause severe toxicity that may even be fatal.  The first symptom you may notice in your horse is onion breath.  Symptoms can then progress to icteric mucous membranes, to abnormal heart and respiratory rates.  Detoxification is key in cases of wild onion poisoning.  There is no antidote so the sooner your veterinarian is able to begin supportive and supplemental therapies in response to your horse’s symptoms, the better his prognosis of recovery.

Wild onion intoxication in horses can cause severe anemia and even death.  If you discover your horse has been ingesting wild onion, contact your veterinarian immediately in order to begin the detoxification process.

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Symptoms of Wild Onion Poisoning in Horses

Symptoms can vary but may include:

  • Onion odor on breath
  • Anemia 
  • Bloody urine
  • Icteric mucous membranes 
  • Weak pulse
  • Increased heart rate
  • Increase respiratory rate
  • Death 

Types

Scientifically, onions belong to the Allium spp. genera.  Species of wild onion can be found in regions of moist areas but most common onion poisoning is caused by ingestion of culled domestic onions.  The wild onion and wild garlic plants are sometimes identified as the same plant.  It produces white to pink/purple flowers on fleshy stems and leaves.  Other common names of wild onion include wild garlic, prairie onion, and Drummond’s onion.

Causes of Wild Onion Poisoning in Horses

Onions produce the toxin N-propyl disulfide in the plant and the bulbs.  In horses, ingestion of large quantities typically cause intoxication but a small amount can still possibly cause symptoms in your horse depending on his health status prior to ingestion.  The toxic alkaloid inhibits certain red blood cell properties.  This leads to malformation of red blood cells and therefore the body removes them naturally from the body system.  With removal of all the malformed red blood cells, anemia occurs as a result.  Rate of ingestion of the wild onions will directly affect the type of anemia your horse is experiencing: mild or severe.

Diagnosis of Wild Onion Poisoning in Horses

To begin her diagnosis, your veterinarian will start by performing a full physical exam.  She will make note of all of his symptoms and get details from you about when they started and if they have been getting worse.  The smallest detail may help her rule out other possible causes of his symptoms.   

She will want to perform lab work so she can check the organ values and levels in your horse’s blood.  She will suggest a complete blood count (CBC) and chemistry panel to check for abnormalities.  Depending on the results, she may want to run more in depth blood related tests.  If the blood work indicates anemia, she may want to create and evaluate a blood smear as well as evaluate your horse’s packed cell volume (PCV).  In cases of wild onion poisoning, the hematocrit count is typically between 10% and 15 % and heinz bodies are found on blood smear.  She may also want to run a urinalysis in addition to the blood work to check kidney function, especially if the urine has a dark color or blood like color to it.  

If your horse is experiencing breathing difficulties and she cannot confirm the cause via auscultation alone, she may want to take radiographs to check his lungs for air, fluid, masses, or other possible abnormalities.  

There may be other tests your veterinarian will want to run in order to rule out other possible causes of your horse’s ailment.  Of course, if your horse dies you can request a necropsy in order to determine the cause.  This will give you a complete diagnosis to ensure none of your other horses suffer from the same illness.

Treatment of Wild Onion Poisoning in Horses

The symptoms your horse is suffering will determine his treatment regimen.  There is no exact treatment your veterinarian can offer your horse.  She can provide supportive therapies and keep your horse comfortable.  She will start fluid therapy to ensure he stays hydrated and to keep his liver, kidneys, and urinary tract flowing.

If he is suffering from breathing difficulties, she may want to supplement him with oxygen immediately.  If this is not an option, she may administer medications to increase red blood cell production and flow in order to keep the oxygen levels in the blood up.  In more severe cases, a blood transfusion may be necessary.

You will need to keep your horse stalled in order to closely monitor him and to keep him comfortable during treatments.  Keeping him calm and stress free is very important for his recovery.  Keeping his heart rate down and oxygen levels sufficient are key.  The more stressed your horse becomes, the more likely his symptoms will worsen

You will need to remove the source of the plant immediately to prevent further ingestion.  Offering your horse a good diet will ensure he does not ingest any more onion plant.

Recovery of Wild Onion Poisoning in Horses

The severity of your horse’s symptoms will play a part in his recovery.  It is possible for your horse to die from anemia and lack of oxygen in his system so the sooner he begins treatment, the higher his chance of recovery.  Keeping wild onion out of your pasture and horse’s diet is ideal.