What you see. The starting point for addressing any equine health related issue is your observation.


Heat, Swelling or Pain at Injection Site


Your horse has been injected with medication or a vaccine and now there is a painful swelling in the area. What should you do?

Swelling and pain at an injection site most commonly occurs in response to a vaccination reaction, or to improper injection technique. Tissue inflammation can occur due to an allergic type response to a substance or vaccine, or due to the irritating nature of the injected substance. In rare cases, tissue infection or bleeding may result. Injection reactions are more common when injection technique is poor.

Mild reactions require little treatment, while more severe reactions may require pain management and other treatment.

  • Code Red

    Call Your Vet Immediately, Even Outside Business Hours
    • If the swelling is large, painful or growing rapidly.
    • If the results of the Whole Horse Exam (WHE) in the resting horse indicate fever (Temp >101F/38.3C) or heart rate greater than 48 BPM.
  • Code Orange

    Call Your Vet at Their First Available Office Hours
    • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.
    • If the swelling is mild or moderate, and not increasing rapidly.

your role


What To Do

Assess your horse's general health using the Whole Horse Exam (WHE), and share your findings and concerns with your vet.

If the swelling is very recent (several hours) you can try applying ice to the swelling. NSAID drugs like phenylbutazone and Banamine® (flunixin meglumine) may be helpful, but should only be given under your vet's guidance.

Some horses that have received an IM injection in the neck are very reluctant to drop their heads to ground level. You may need to raise feed or water to ensure the horse can comfortably reach it.

your vet's role

Your vet will assess the horse's general health and carefully evaluate the area to determine the need for local treatment. In rare cases, abscess drainage may be required. They will provide a plan for supportive care until the problem has resolved.

If the reaction is the result of a vaccination that you gave, tell your vet. They will keep a record of this reaction to prevent similar problems in the future. They will also discuss vaccine alternatives with you.
Questions Your Vet Might Ask:
  • When was the horse injected?
  • What medications or vaccines were given?
  • Did a veterinarian give the injection(s)?
  • Do you know what vaccine or medication caused the swelling?
  • Are other horses affected?
  • What are the results of the Whole Horse Exam (WHE)?

Author: Doug Thal DVM Dipl. ABVP