A Balanced Calcium:Phosphorus Ratio Will Help Prevent Skeletal Issues in Your Horse

Why are Calcium:Phosphorus ratios important?

Last post we talked about the problem with bran mashes and touched on some issues with calcium:phosphorus ratio imbalance (big head disease). Today I want to take a closer look at why this mineral ratio is so important.

Importance of Calcium

Around 99% of calcium found in the body is found in the bones and teeth of your horse, yet only 35% of equine bone is comprised of calcium. The rest of the bone is made up of other minerals. The other 1% of calcium in your horse’s body plays a vital role in muscle contractions, blood coagulation, enzyme regulation and cell membrane function. Therefore, proper calcium levels in the body are essential to your horse’s health and wellbeing. 

Importance of Phosphorus

Phosphorus is another major component of bone, making up around 14-17% of the equine skeleton. Additionally, it is required for the energy transfer process with adenosine diphosphate (ADP) and adenosine triphosphate (ATP). For those who took high school biology, you should remember ATP as the molecular source of energy in our bodies. Finally, phosphorus is important for the production of phospholipids, nucleic acids and phosphoproteins which all play important roles in healthy cell function. 

Calcium Deficiency

The body pulls calcium out of the bones when blood calcium levels drop too low. This can cause weakness in your horse’s skeleton if done in excess. Calcium deficiency in foals can lead to metabolic bone diseases, enlarged and crooked joints. In mature horses it can lead to osteoporosis. Calcium deficiency cannot be tested for in blood as the body will usually pull enough calcium into the blood from the bones to have normal levels, even if they are chronically deficient. 

Calcium Excess

Unnecessarily high calcium levels have been implicated in gastric ulcers and should be avoided. Implicated, however, does not mean it causes them, and ulcers are a more complicated issue than just a little calcium excess. Long term excess calcium can result in hypercalcemia, however this is rare.

Phosphorus Deficiency

Phosphorus deficiency in growing horses can cause bone weakness, enlarged joints and crooked long bones. In mature horses it can lead to a softening and weakening of the bones. 

Phosphorus Excess 

Excess phosphorus reduces the rate of calcium absorption which leads to chronic calcium deficiency and nutritional secondary hyperparathyroidism. 

Sources of Calcium

Hay and fresh pasture contain calcium, especially alfalfa hay. As an exception, Orchardgrass contains an inverted calcium:phosphorus ratio. The amount of calcium in hay and pasture varies depending on the type of hay, soil quality, plant maturity and hay quality. Calcium is easier for a horse to digest from alfalfa grass than from other grass hay sources such as Bermudagrass.

Sources of Phosphorus

Hay and pasture contain low but adequate levels of phosphorus. Grain feeds and grain-based feeds such as sweet feeds, wheat bran and oats contain large amounts of phosphorus. Raw grains, especially in the form of green feeds or wheat/oat/barley based hays usually fed to cattle contain high phosphorus levels and long-term feeding of these forage source can risk your horse developing nutritional secondary hyperparathyroidism. 

Calcium to Phosphorus Ratio

It is important that your horse intakes adequate amounts of calcium and phosphorus in their diet. The ideal calcium:phosphorus ratio is generally regarded as 2:1, meaning double the amount of calcium than phosphorus. However, a range of 1.4:1 to 2.6:1 is acceptable as achieving the exact 2:1 ratio is nearly impossible when balancing a horse's diet. Ratios of less than 1:1 or more than 6:1 can cause major health issues. The exact amounts required by your horse will depend on their age, size, workload, if they are breeding, and any other health issues they may have. If you are unsure about the calcium:phosphorus ratio in your horse’s diet it is best to check with your veterinarian or a qualified equine nutritionist. 

Reference

National Research Council. (2009). Nutrient Requirements of Horses. Sixth revised ed. 

Image: Anneke Saveur