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Home:Equine Diseases:Fibrous Dyspasia

Equine Diseases - Fibrous dysplasia



Equine Fibrous dysplasia is better known as equine juvenile mandibular ossifying fibroma.

Fibrous dysplasia is a chronic disorder in the form of a benign bone tumour which usually occurs in the lower jaw/mandible of young horses between the ages of between two and fourteen months of age. The tumour can grow to quite a large size.

The lesion-like tumour causes swelling and weakening of the areas of bone affected.

If action is not taken, the tumour will most likely grow so large as to make eating and drinking almost impossible for your horse.

All breeds and genders are susceptible to Fibrous dysplasia with the emphasis being on young horses.


  • Firm bony mass on the horse's lower jaw
  • No pain when manipulated
  • Teeth may be loose upon palpation
  • Weight loss as a result of difficulty in eating. 
  • Difficulty when trying to grasp things in the jaw
  • Enlargement of the lymph nodes


The exact causes of Equine Fibrous dysplasia are not known, but the following are generally believed to be the main causes.

  • a chemical irregularity in a specific bone protein perhaps caused by a gene mutation at birth
  • Injury such a fall, kick or collision with an object could weaken the jaw and render it more liable to minor injury.
  • Trauma this could stimulate the growth of the tumour in the injured jaw


Your vet will quickly recognise Equine Fibrous dysplasia but will probably want to do some tests to ascertain the exact type of tumour. It is very important to get the full picture as there is a high reoccurrence rate if the entire tumour is not removed. This will be done by either

  • a core biopsy
  • an en bloc excisional biopsy
  • X-ray
  • Computed Tomography Scan more commonly known as a CAT scan
  • Blood tests

Treatment for the Equine Fibrous dysplasia will then be decided and could be either surgery to remove the tumour, radiation therapy to make sure that all of the abnormal cells have been killed, or a combination of both these therapies.

If the entire mass is removed successfully it is very unlikely that the juvenile ossifying fibroma will reoccur.  

While the surgery seems radical, horses react well to it providing that afterwards, (a) you ensure your horse's diet is suitable and (b) you pay meticulous attention to your horse's dental care. Your veterinary surgeon will be you very specific help in these areas.