Nutritional Secondary Hyperparathyroidism (NSH) or more commonly known as “Big Head” in horses is caused by a calcium deficiency. The disease is preventable and treatable, but if not addressed it can be very painful and subsequently lead to death.
A veterinarian will be able to diagnose Big Head through physical examination of the horse and by analysing the horses feed and/or pasture they are on. The following are signs and symptoms seen in a horse suffering from Big Head which will often become more severe as the disease progresses.
- Swelling of the facial bones, particularly the jaw, usually symmetrical on both sides
- Weight loss
- Pain when eating
- Loose teeth
- Lameness, shortened or stiff gait
- Noisy breathing or difficulty breathing from airway obstruction due to swollen bones
- X-rays can show changes in the bone, being less dense and giving a more porous appearance.
Big Head can be prevented and treated by correcting the nutritional imbalance. A calcium deficiency can occur through not enough calcium in the diet, an imbalance in the calcium to phosphorous ratio and/or inadequate absorption of calcium.
The calcium to phosphorus ratio in a horse’s diet should ideally be 2:1 and not drop below 1:1. When the phosphorous in the diet becomes more than the calcium it can inhibit the absorption of calcium and magnesium and cause a deficiency. Inadequate calcium absorption often occurs when horses are grazing on pastures that contain high oxalate levels. Such pastures include buffel, kikuyu, setaria and green panic grasses. The oxalate molecules in the grass bind to the calcium preventing it from being able to be absorbed.
A standard horse requires approximately 20-25g of calcium per day, with lactating mares and young growing horses requiring more. This calcium can be achieved through feeding a balanced complete feed and/or adding a calcium supplement to the horses diet.
If you think that your horse is suffering from Big Head or unwell please contact your veterinarian for advice.
Originally published in My Pet Magazine Issue 11.
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