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Mineral Nutrition - “The Importance of Calcium and Phosphorus”

Minerals are inorganic substances that are needed by the horse. Minerals play important roles in the acid-base balance, formation of bones, teeth and other structural components, are co-factors to aid in enzyme function and for normal metabolic and biological activity. Unlike vitamins, minerals cannot be created by the horse; thus, they need to be supplied in the diet. The Nutrient Requirements of Horses (2007) lists requirements for 14 individual minerals. Fortunately, most common feeds (hay/pasture/whole grains) contain a variety of important minerals. The mineral content of these feeds varies depending on the mineral content of the soil in which the feed is grown, type of plant and even the time and maturity of the plant when harvested. Therefore, it is customary to add minerals to commercial horse feeds to correct for regional mineral deficiencies. Although minerals are needed by the horse, they should only be supplemented to correct for specific mineral deficiencies in a diet. Too much mineral supplementation is as detrimental as too little.

Types of Minerals

Minerals are often divided into two categories. The term “macro-mineral” is used to describe minerals that are required in large amounts in the diet. Examples of macro-minerals include calcium, phosphorus, magnesium, potassium, sodium, chlorine, and sulfur. The term “micro-mineral” is used to describe minerals that are required in small amounts in the diet. This does not make these minerals any less important, they are just required in smaller amounts. Examples of micro-minerals include cobalt, copper, iodine, iron, manganese, selenium, and zinc.


Two of the Most Important Minerals – Calcium and Phosphorus

Calcium 99% of the calcium within the horse’s body is found in the bones and teeth. In fact, bones typically contain a whopping 35% calcium. Thus calcium serves a huge role in the structural integrity of the skeleton. Calcium also plays a critical role in muscle contraction, blood clotting and enzyme regulation. As calcium is involved in so many bodily functions, the level of calcium in the blood is tightly regulated. Calcium moves into and out of the blood by being absorbed from the digestive tract, eliminated in the urine or feces and mobilized from or stored in the skeleton. One of the most commonly fed sources of calcium in the diet is Lucerne. The concentration of calcium in Lucerne is quite high, generally greater than 1% calcium and is highly digestible to the horse. Other sources of calcium, such as calcium carbonate, are typically added to commercially prepared feeds.

Phosphorus Like calcium, phosphorus is a major structural component of bone. A typical bone contains 14-17% phosphorus. Another major function of phosphorus appears in energy generation reactions within the body. The currency used for the reaction that turns chemical energy into mechanical energy requires phosphorus. Finally, phosphorus is a component of many lipid molecules that form membranes. The phosphorus that is contained within plants is not very digestible for horses. Instead, inorganic sources are better utilized and are added to commercial feeds.

Calcium and Phosphorous deficiency and requirements

Mature horses that do not get enough calcium or phosphorous in the diet will have a weakened skeleton and are susceptible to lameness. A mature, 500 kg horse that is not working, pregnant or lactating requires approximately 20 grams of calcium and 14 grams of phosphorous per day. The requirements for both minerals increase for exercising horses, pregnant mares and lactating mares. The highest daily calcium and phosphorous requirement is for lactating mares immediately after birth of their foal. A 500 kg lactating mare requires approximately 85 grams of calcium and 39 grams of phosphorous per day. Young, growing horses that do not get enough calcium and phosphorous will suffer from bone anomalies and ailments that may derail the future performance potential of the horse. A young, growing horse with an expected mature weight of 500 kg will require between 36 to 40 grams of calcium and 20 to 22 grams of phosphorous per day.


The Calcium: Phosphorus Ratio

Before we worry about having the correct ratio of calcium to phosphorus we first need to assure that the absolute requirement for calcium and phosphorus is satisfied. Once the requirement for both minerals is satisfied, we can consider the ratio. Increased amounts of total phosphorus in the diet compared to calcium, interferes with the absorption of calcium and results in severe bone problems, such as Nutritional Secondary Hyperparathyroidism (NSH). This disease results in calcium mobilized from the bone and is characterized by lameness and enlargement of the upper and lower jaw as the calcium in the jaw is replaced by fibrous connective tissue. A maximum ratio of 6 parts calcium to 1 part phosphorus has been feed to young, growing horses without growth problems. However, a ratio of 2 parts calcium to 1 part phosphorus is considered the ideal dietary ratio. Ironically, this is the same concentration of calcium to phosphorus found in bones.

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