Big Head is a common term for a condition seen in horses due to eating a diet made up of predominantly Buffel Grass. The scientific name for Big Head is, "Nutritional Secondary Hyperparathyroidism" THE THING IS, there are lots of other plants which can cause "Big Head". These are: - Pangola grass - Guinea grass - Para grass - Signal grass - Purple pigeon grass - Kikuyu grass These grasses belong to a class of plants called "soluble oxalate grasses". In short - the soluble oxalates in these plants stop the horse from absorbing calcium from their diet and causes them to draw calcium from their bones instead. The bone develops fibrous connective tissue >> the bone "swells" or appears larger. The head and pelvis are commonly seen to be the areas of bone that are most affected, hence the name "Big Head". Other signs seen with Nutritional Secondary Hyperparathyroidism are ill thrift and lameness. To reduce the risk of your horse getting Big Head you can do the following: - Avoid grazing your horses on paddocks predominantly made up of these grasses for a minimum of 1 month - If you can't avoid grazing them, feed a calcium and phosphorous supplement (dosing can be specific to case) - Use mix of safe pasture grasses and legumes in the paddock Once treatment and medical management is started, it can take anywhere from 4-12 months to see improvements.