The most important in a horse's diet is his intake of phosphorous in comparison to calcium. It should be no more than two parts calcium to one and a half parts phosphorous. Excess phosphorous can cause many problems like binding up calcium, causing a deficiency, and can also upset the metabolism of the animal. An imbalance of calcium and phosphorous can be responsible for ringbone, splints, spavin, lameness, abnormal bone growth, especially in growing animals and also enlargement of the jaw and face bones known as bighead disease.
This is a reproduction of an article written by Bud Wrona as it was published for the local Redmond (WA) paper, in a column titled "Off the Hoof," which was created to help educate the community on, mainly, the proper care and feeding of horses. Some of the information might be outdated (unfortunately, we don't have the original publish dates) so please leave a comment if you happen to notice something that is.