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

Your vet may diagnose

Big Head or Bran Disease

Synonyms: Miller's Disease, Nutritional Secondary Hyperparathyroidism, Osteodystrophia Fibrosa


This is an uncommon nutritional imbalance seen more frequently in growing horses. It is caused by excessive phosphorus in the diet without adequate calcium. Calcium and phosphorus together make up the inorganic part of bone. If this calcium/phosphorus imbalance exists, it disrupts the normal balance of bone resorption and deposition. Bone density is lost and bones become thicker to compensate for weakness.

Signs of this disease include shifting leg lameness (thought to occur because of abnormal bone turnover and tiny microfractures within the bone), and symmetrical enlargement of the facial bones - hence the name "Big Head". It can also cause difficulty eating because of changes in the bone of the tooth sockets. Bone fractures and heart failure may result.

Cereal grains like oats, corn and red bran are high in phosphorus and not calcium.

Veterinarians diagnose this condition with a careful history, specifically noting diet/feed, appearance and physical exam. Blood and urine levels of calcium and phosphorus are also helpful in diagnosing this condition.

Treatment involves diet change to normal calcium to phosphorus ratio. It may take months for any change in appearance of the skull bones.

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 generally good with calcium supplementation but the changes in the bones may take weeks to show obvious improvement. Some facial abnormalities may be permanent.

my role


I might observe

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

Very Common
Less Common
more observations

Questions To Ask Your Vet:
  • Why did this occur?
  • How should I change feeding & management for all my horses?

Ensure that horses are fed adequate calcium, especially if their diet is high in phosphorus.

Related References:

Verwilghen. "Help Doc: My horse turned into Frankenstein." Department of Large Animal Sciences, Faculty of Health and Medicine, University of Copenhagen, Denmark.

Author: Doug Thal DVM Dipl. ABVP