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A swollen-face, dull coat, shifting lameness, bunny-hop canter…are any of these signs familiar? If so your horse may suffer from a disorder described as ‘Big Head’. ‘Big Head’ is a calcium deficiency disease induced by a diet with a persistent lack in calcium, excess in phosphorus and/or imbalanced calcium to phosphorus ratio. This disorder has severe effects on horses including difficulty breathing, painful movement and lameness. Being a nutritional related disease, it can easily be prevented and treated by correcting the imbalance in your horse’s diet.
What is Big Head?
Nutritional Secondary Hyperparathyroidism, commonly known as ‘Big Head’, is a severe calcium deficiency in horses caused by a diet low in calcium, excessive in phosphorus, or with a calcium to phosphorus ratio less than 1:1. In order for horses to maintain their blood calcium levels, they will mobilize mineral from their bones in cases where the calcium intake via the diet is limited. It is important to note that calcium plays a huge role in the structural integrity of the horse’s skeleton, with 99% of the total calcium within the horse’s body found in the bones and teeth. During prolonged calcium deficiency horses mobilize large amounts of bone mineral primarily from their facial and pelvic bones which become fragile and fibrous connective tissue develops. This fibrous tissue causes their facial bones to swell, giving them a ‘Big Head’ appearance. Young horses are most prone to this facial swelling as their bones have not completely formed and hardened.
Horses that have a severe calcium deficiency can exhibit a number of symptoms which may increase as the disease progresses, including:
Horses require a specific amount of calcium in relation to phosphorus in their diet, as increased amounts of phosphorus compared to calcium interferes with the absorption of calcium. A ratio of 2 parts calcium to 1 part phosphorus is considered the ideal dietary ratio and coincides with the concentration of calcium to phosphorus found in bones. The dietary ratio should not be lower than 1:1. Horses develop ‘Big Head’ due to two main reasons, both of which are related to their diet:
This calcium deficiency disease can be detected through a physical examination of your horse by a veterinarian in combination with a diet analysis.
Prevention and Treatment
Horses affected can be treated by correcting their dietary imbalance. The strategy to prevent or treat ‘Big Head’ depends on the cause:
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