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What is Nutritional Secondary Hyperparathyroidism?

Nutritional secondary hyperparathyroidism in horses is also known as big head or bran disease.  As noted above, the secondary hyperparathyroidism is a bone condition caused by a calcium deficiency.   This disease is found to afflict young horses who may present with lethargy, stiffness, noisy breathing, and poor body condition.  It is a nutritional based disease that is directly affected by the ratio of calcium and phosphorus in the horse’s diet and can be the cause of tiny fractures in the weakened bones.

The definition of secondary hyperparathyroidism (NSH) is a metabolic bone disease of horses caused by calcium deficiency.  Horses who are younger than 7 years seem to be the most frequently afflicted.

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Symptoms of Nutritional Secondary Hyperparathyroidism in Horses

The symptoms that you will likely notice for NSH in your horse are:

  • Lameness specifically with a shortened gait and tenderness
  • Appearance of stiffness
  • Swelling of facial bones, thickened jaw bones, difficulty chewing
  • Loose and shifting teeth
  • Obstruction of nasal passages, possibly causing noisy breathing and possible discharge
  • Ruptured tendons with increased risk of fractures
  • Weight loss
  • Poor body condition
  • Lethargy
  • Decreased growth 

Some of the earliest symptoms (lameness and tenderness) may be difficult to spot since these are also symptoms of young horses who are still growing and entering into training and exercise routines.

Types  

There is only one type of nutritional secondary hyperparathyroidism but this disease has other names to which it is referred:  

  • Big head disease
  • Bran disease
  • Miller’s disease

These names are attributed to nutritional secondary hyperparathyroidism because of the symptoms which are displayed by the afflicted horse (big head) and the feed (bran) which is causative of the condition.

Causes of Nutritional Secondary Hyperparathyroidism in Horses

The cause of nutritional secondary hyperparathyroidism is nutritional in nature. It is an imbalance between calcium and phosphorus in the diet of the horse.  Horses commonly afflicted with NSH are those who graze entirely on grasses which contain a substance called oxalate which inhibits the absorption of calcium in the horse’s digestive tract.  Oxalate is defined as “any salt occurring in plants, especially spinach, rhubarb and certain other vegetables and nuts, and capable of forming an insoluble salt with calcium and interfering with its absorption by the body”. The horse’s body needs the calcium to function so it is taken from the bones and replaced with fibrous connective tissue.  This causes the horse’s head to increase in size. 

Not just the ratio of calcium to phosphorus but also low calcium in the diet (or the inability of the horse’s body to utilize the calcium in the diet) begins a cycle in which the horse’s body literally “mines” the calcium from the bones so that a normal level of calcium can be maintained in the blood.

Horses who consume a diet that consists mostly of grains which are higher in phosphorus and lower in calcium are at higher risk.  The phytates in bran also bind up the calcium and inhibit its absorption by the intestinal system during the digestive process. Basically, equine diets which consist of hay and pasture forage and cereal grains are the ones which lend themselves to the development of nutritional secondary hyperparathyroidism in horses.

Diagnosis of Nutritional Secondary Hyperparathyroidism in Horses

Here are some of the steps to expect in the diagnostic process:

  • Your veterinary professional will need a complete and thorough history from you in addition to his thorough and complete physical examination of your horse  
  • During his examination, he will be noting the clinical signs which your horse is exhibiting 
  • He will need to evaluate the diet being fed to your horse; diets which consist of primarily hay and pasture forage and cereal grains will be more likely to contribute to the development of NSH  
  • He will need blood tests to determine the levels of at least the calcium and phosphorus in the blood of your equine 

Once all of this information has been obtained, your veterinary professional will develop an appropriate treatment plan to readjust the balance of calcium and phosphorus in the horse’s diet to allow the “mining” of calcium from the bones to stop.

Treatment of Nutritional Secondary Hyperparathyroidism in Horses

Once diagnosed, the treatment that will most likely be recommended for your equine for NSH will be a multi-step process:

  • A maintenance level of calcium will be determined by your vet and this level will be used to gauge and adjust the dietary intakes recommended
  • For the first 2 weeks, he will likely recommend upping the calcium intake to be equal to 2 or 3 times the maintenance level he has established
  • The maintenance ratio of calcium to phosphorus will need to be restored and there will likely be a recommendation to increase the calcium intake so this restoration can happen
  • A specific period of stall rest
  • Administration of NSAIDs
  • If the horse is grazing in pastures containing oxalate plants, you will be asked to remove the horse from access to those pastures 

The good news about nutritional secondary hyperparathyroidism is that it is easy to treat, usually requiring only dietary changes to restore the natural calcium to phosphorus ratio and increase the calcium in the diet.

Recovery of Nutritional Secondary Hyperparathyroidism in Horses

The prognosis for older horses to recover fully from NSH is very good.  The danger of this disease exists for younger horses whose bones are still in the development process.  This disease can affect the growth of the long bones in younger horses and the degree of seriousness will depend on how much damage has taken place in the bones.  It becomes incumbent upon the owner to be watchful and informed about the dietary needs of the horses in their herds, especially as they apply to young, growing horses.  The simplest method for you, the owner, to avoid this malady in your herd, especially in the younger ones, is to be sure to feed your herd a diet in which the calcium and phosphorus ratios are appropriate.  This is much easier to do today than for those owners having herds in the early 1900’s as much of the feed available today has been supplemented with calcium to ensure the calcium to phosphorus ratio are appropriate.  

Also ensuring that your herd has enough calcium in their diet is just as important as maintaining the appropriate calcium to phosphorus ratio. Though NSH is more rare as a result of these fortified feeds, it behooves you, the owner, to make yourself aware of the symptoms and intervene as early as possible if they are noted in any of your horses, regardless of age.