Big Head in Horses

Many would have heard of the term Bighead especially if you happen to live in an area with a lot of tropical grasses. Big Head refers to a condition that affects horses suffering from long-term calcium deficiency. It can affect the horse in many ways, and can eventuate into severe illness. The good news is it can be easily managed with a carefully balanced diet.

What is Bighead?

Scientifically referred to as Nutritional Secondary Hyperparathyriodism, Big Head is caused by a diet low in calcium. The condition can also be related to excessive phosphorus or an incorrect balance of the Calcium to Phosphorus ratio.

So why is this ratio so important?

Increased levels of phosphorus in comparison to calcium limits the horses’ ability to absorb calcium, ideally the ratio should be 2:1 (2 parts Calcium to 1 part Phosphorus). This ratio mirrors the levels found in the horses’ own bones. Where the ratio is seen to reach levels near 1:1, symptoms of Bighead may start to occur.

What are the symptoms and how are they triggered?

  • Swollen facial bones, especially around the upper jaw or nasal bone
  • Painful joints
  • Loss of body condition
  • Lameness/stiffness across the body
  • Increased noise when breathing, due to swelling of the nasal bones
  • Dental pain

If a horse’s diet is deficient in calcium over time it will compensate by taking what it needs from its bones, primarily from its facial and pelvic bones. These structures then become weak and fibrous tissue begins to develop. As a result, this causes the facial bones to swell hence causing “Bighead” syndrome.

There can be two main causes of a horse suffering from Bighead

  • Imbalanced diet (calcium/phosphorous ratio)
  • Grazing on pasture high in oxalates

Oxalates found in certain grasses bind calcium in the plant, this prevents a horse from being able to absorb calcium from the grass during digestion. Grasses high in oxalates include tropical species, such as Setaria, Kikuyu, Buffel, Para Grass, and Green Panic.

How can we prevent and/or treat Big Head?

  • Having a correct and balanced diet for your horses’ needs will assist with treating and preventing Bighead, aiming for a Calcium to Phosphorus ratio of 2:1. Ranvet have a free diet evaluation service that can assist you with this! You can submit your current diet online at and one of our nutritionists will personally review your diet, providing a report and any necessary recommendations, free of charge!
  • Supplementing your horses’ diet with a high-quality calcium supplement, such as Ranvet’s Folactin Red, which is specially designed to aid in the absorption of calcium and balance the calcium to phosphorus ratio.
  • If your horse is grazing pasture that does have grasses high in oxalates, adding Lucerne to their diet can also help. Lucerne is high in calcium and can be very beneficial in areas high in oxalate grasses.

Calcium plays a big role in a horses skeletal system a deficiency can lead to the weakening of the bone structure and bone density. Therefore, it’s extremely important to get the balance correct! With the right management and dietary attention, you can actively prevent the risk of Bighead development, and keep your horse at its healthiest and happiest!

Written by Selena P.


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