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Understanding Big Head in Horses



Big head, also known as nutritional secondary hyperparathyroidism, is a condition that affects horses, particularly those on a high grain diet low in calcium and high in phosphorus, or horses on oxalate pastures. This imbalance disrupts the normal regulation of calcium and phosphorus in the horse's body, leading to bone demineralisation. In short, they rob their own bones to keep the right amount of calcium in their blood.


High-oxalate grasses include Setaria, Buffel Grass, Kikuyu, Purple Pigeon, Green Panic, Pangola Grass, Para Grass, and Signal grass. These grasses contain high levels of oxalate that bind most of the calcium in the grass, making it unavailable for absorption when the horse eats it. 



It’s important to note that horses grazing on high-oxalate pastures can become severely calcium deficient. Therefore, careful management and adequate calcium supplementation are necessary when horses are grazing on these types of pastures.


Signs and Symptoms


Big Head (literally swelling of the bones in the face) is not the only symptom of calcium deficiency. Other signs include: 


  • Lameness: Horses may appear stiff and have a shortened gait.

  • Ill-thrift: Loss of condition even though they have access to ample feed.

  • Chronic or recurrent limb or back/neck injuries or pain.

  • Early onset of arthritis.

  • Poor hoof quality.

  • Frequent sport injuries (ligament, joint and bone).

  • Bone spurs.

  • Stringhalt.

  • Neurological symptoms (weakness, impaired gaits, vertigo, etc.).


Prevention and Management


Prevention - If your horse grazes on these pastures, you can supply your horse with additional feeds high in calcium. Lucerne hay and beet pulp are both high in calcium.  Grains and brans tend to be high in phosphorous, which competes for absorption with calcium, so you want to avoid contributing to the problem by feeding those.


If your horse already has Big Head or symptoms of calcium deficiency, you can increase calcium in the diet with supplementation such as Sound Advice Trace Mix with Calcium. At only $15 for one month's supply this is cheap insurance against mineral deficiencies.






Big Head is not the only condition arising from deficiencies in pasture.

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