Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose


Synonyms: Anaphylactic Shock


Anaphylaxis (anaphylactic shock) is a rare but potentially severe and life-threatening, body-wide allergic response. It is most commonly seen in horses after they have received an injection of a medication or vaccine, but it can be a response to any allergen, like an insect sting.

Signs begin within minutes to hours after injection. The condition is sometimes confused with injection reactions, like procaine reaction or intracarotid injection. Anaphylaxis is a true allergic reaction, whereas a procaine reaction is a neurologic reaction to the penicillin carrier procaine. It usually takes longer to develop than these other conditions.

Horses with modest anaphylaxis usually get hives and/or face/head swelling. Those with more severe anaphylaxis look severely distressed. They are off feed and depressed; they usually stand head low, nostrils flaring, with rapid respiratory and heart rates. They may make respiratory noise and seem to have difficulty breathing. They may develop diarrhea or show colic signs. Severe cases will go into shock and die if they don't get veterinary help right away.

Diagnosis is usually clear from these signs following recent use of medication. If no medication has been given recently, then anaphylaxis can be hard to differentiate from colitis, an attack of RAO or other severe and acute systemic disease.

Treatment starts with recognition of the condition. Intense nursing care, steroids, NSAIDS, and intravenous fluids. Epinephrine and other emergency medications might be needed.

my vet's role



Other conditions or ailments that might also need to be ruled out by a vet.

Very Common
Less Common
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The prognosis is fair with vet treatment.

Success depends on the severity of the case, prompt diagnosis and aggressive treatment.

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
Less Common
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Questions To Ask Your Vet:
  • Why did this happen, what is the cause?
  • What needs to be avoided to prevent this in the future?
  • Should I have medication on hand to administer in case of another allergic reaction?

Once a horse has had anaphylaxis, it is critical to prevent exposure to the same allergen again. So identifying the cause, if possible, is very important.

further reading & resources

Related References:

Orsini JA, Divers TJ Equine Emergencies- Treatment and Procedures 3rd edition. Saunders

Author: Doug Thal DVM Dipl. ABVP