What is the calcium:phosphorus ratio and why is an acceptable ratio so important to horses?
The calcium:phosphorus ratio is the amount of calcium relative to phosphorus in the diet. For example, a grass hay might contain 0.4% calcium and 0.15% phosphorus. The calcium:phosphorus ratio is 2.6:1. The reason the ratio is important is that calcium and phosphorus are laid down in bone in approximately a 2:1 ratio. That is why many nutritionists recommend a 2:1 calcium to phosphorus ratio in a horse s diet. However, we know that mature horses can tolerate a wide range of calcium:phosphorus (1:1 to 8:1) with no clinical problems. Young horses should have a narrower range e.g. (1.5:1 to 3:1) because their bones are actively growing. Not only is the ratio important, it is also important that the diet has enough calcium and enough phosphorus. For example, a foal s diet should have 0.7% calcium in the diet and 0.4% phosphorus. If using the grass hay from above, its ratio is okay but there is not enough of either mineral to meet the growing needs of the foal.
