If you live in an area geographically rich in phosphorus (such as in Central Kentucky), your horse will likely consume more P than he or she needs, even from forage alone. | Photo: iStock

It is only appropriate to follow last month’s column on calcium (Ca) with its sidekick, phosphorus (P). Phosphorus is the second-most abundant mineral in the horse’s body; about 80% of it is found in horses’ teeth and skeleton.

Calcium and phosphorus are very closely linked, because Ca combines with P to form hydroxylapatite, found in bone and teeth. A dietary deficiency or excess of either one can interfere with the other’s absorption and utilization. As such, when evaluating a diet, ensuring that the P and Ca requirements are met is important, but making sure the horse is consuming an appropriate ratio of Ca to P in the total diet is paramount.

Your horse’s total dietary Ca:P ratio should not drop below 1.1:1 (National Research Council’s Nutrient Requirements of Horses, 2007; NRC). Typically, unfortified grains (e.g., oats or corn) naturally contain more P than Ca. Additionally, if you live in an area geographically rich in P (such as Central Kentucky), forages also tend to contain higher amounts of P. In some cases, a grass forage’s P content can even exceed the Ca content. In cases where the Ca:P ratio drops below 1.1:1, additional Ca will be needed in the diet to improve the total dietary Ca to P ratio. You can accomplish this by adding legumes or Ca-fortified concentrates