Bighead Disease: What is it, and should you be worried?

We have all heard that ensuring that our horse’s diet is balanced is crucial for their well-being, and this is especially true for ensuring that your horse does not suffer from Bighead Disease. Bighead Disease is due to inadequate absorption of calcium, usually due to horses grazing high oxalate pastures or being fed diets high in phosphorous to calcium. Luckily, Bighead Disease can be easily prevented and treated by supplementing your horse with additional calcium.

What is Bighead, and why does it occur?

As mentioned above, Bighead disease, also known as Nutritional Secondary Hyperparathyroidism, is caused by a diet that is low in calcium or has excessive amounts of phosphorous. Horses maintain 99% of the total calcium within their bodies in their teeth and bones. Also, having an adequate blood calcium level is vital for cellular function, blood clotting and nerve, cardiac and muscle function. Generally, when calcium blood levels fall, the body will reabsorb the calcium through the kidneys and gut. But, if the horse is not absorbing enough calcium via these mechanisms, usually due to the calcium being bound to oxalates, the horse will reabsorb calcium from the bones. Once this occurs, usually in the facial and pelvic bones, the horse will have significantly weakened bones and fibrous tissue develop. The fibrous tissue causes the bones to swell, usually in the face, which gives them a Bighead appearance. 

Bighead is often seen in horses grazing high oxalate pastures such as Kikuyu, panic, buffel and Setaria grasses. The oxalate in high oxalate pastures attaches to the calcium in the horse's gut, forming calcium oxalate, which prevents the horse from absorbing calcium. So, even if the horse is receiving an adequate amount of calcium in their diet, they may not be absorbing the calcium, which can lead to big head. 

Big head disease can also be caused by feeding a diet too high in phosphorous and low in calcium. An example is a diet high in bran and grains. Bran and grains contain phytates which bind to calcium similarly to oxalates, stopping the absorption of calcium by the horse. The optimal diet should have two parts calcium to one part phosphorous and no lower than a ratio of 1:1. 

What are the clinical signs?

There are several symptoms a Bighead-affected horse can present, which include:

• May lose weight and have a coarse, stark coat whilst being maintained on a seemingly adequate diet;
• Swelling of the facial bones usually presents symmetrically and is due to calcium resorption 
• Difficulty breathing due to a narrowing and obstruction of the nasal passages
• Presentation of tooth pain, loose teeth and difficulty eating 
• Lameness or a stiff gate due to weakened bones 

If you suspect your horse has Bighead Disease, it is recommended that you consult with your veterinarian and also run a complete diet analysis. 

How do we prevent and treat Bighead?

Luckily, Bighead Disease can be treated and prevented through diet. Horses that are grazing high oxalate pastures and those that have clinical signs of bighead disease should be supplemented with additional calcium. Ideally, calcium carbonate should be used over dynamite, as the ratio of calcium is much higher. Horses with bighead also tend to develop a phosphorous deficiency, so supplementation with dicalcium phosphate is ideal. Horses can also be fed Lucerne hay, as it is high in calcium. 

My horse grazes in a high oxalate pasture; help!

First things first, don't panic! If you can't change your horse's pasture, then you will need to ensure that your diet has adequate levels of calcium. Adding calcium carbonate and calcium phosphate to your horse's diet will help on ensuring sufficient amounts of calcium are absorbed. 

If you need any help in sourcing a calcium supplement, we stock both calcium carbonate and calcium phosphate, or you may like to choose a premade product such as Kohnkes Own Cal-Xtra. We are always here to help, so please visit us in-store or online.