Big Head is a calcium deficiency of horses and donkeys grazing introduced tropical grass species.  It is caused by crystals of calcium oxalate in the grass blades that prevent absorption of calcium from the grass during digestion. Clinical signs may include swelling of the jaws and facial bones, shifting lameness, abnormal breathing, dull coat, ill-thrift or weight loss. 



Allow grazing on native grasses where possible. Avoid grazing horses and donkeys on introduced tropical grasses for more than a month at a time.  These grasses are Setaria, Buffel,  green panic, kikuyu, guinea, papa, pangola and signal grasses.  If only hazardous grasses are available, try encourage the growth of a legume component in the pasture such as clover which is high in calcium and free of oxalate, and feed a calcium and phosphorus supplement.

An effective and affordable way to provide the required amount of calcium and phosphorus is as follows:



How can Big Head be prevented?

Big Head in Horses and Cattle

This amount of supplement should be consumed per week per average sized horse to prevent Big Head. It is preferable to supplement your horse on a daily basis, so divide this amount by seven to be fed daily i.e approx 170 grams/day. Molasses can be used as a carrier to make the supplement more palatable if needed.   

Because of their smaller size, feed donkeys and ponies a proportionately smaller ration.  Other calcium supplements are available, but may not contain the correct calcium:phosphorus ratio or may not be as cost-effective as the mixture listed above.

Please note the above recipe contains limestone but there are various other types of "lime" primarily used in construction that are caustic and would be harmful if fed to your horse; these unsuitable limes include hydrated lime or slaked lime (calcium hydroxide), quicklime or unslaked lime (calcium oxide), or agricultural lime (often contains quicklime). 

* Make up 1.2 kg of a mixture containing 1/3 ground limestone (calcium carbonate) and 2/3 DCP (dicalcium phosphate).

Can Big Head be cured?

Big Head can be cured and our veterinarians can advise on treatment for this condition. Recommendations will include doubling the amount of mineral supplements listed above for a period of at least 6 months in order to replace the mineral lost from their bones, and ensuring that no grasses containing oxalate are fed to the horse.