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Calcium and Phosphorus requirements in horses

Calcium and Phosphorus

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Calcium and phosphorus horse

The organism of horse contains about 22 known minerals, most of which are essential for life. This means that, if deficient, they can seriously compromise the health of the horse, putting it in danger of life.

Among minerals, we know macro- and micro-elements according to their requirements in the daily ration.

Calcium and Phosphorus are two macro-elements, like Sodium, Chlorine, Potassium, Magnesium and Sulphur.


Calcium is certainly the most present mineral in the body of the horse and its almost totality is found in the skeleton and teeth; in addition to this structural function, it is involved in the transmission of nerve impulses, in blood clotting, in muscle contraction and regulates intra- and extracellular flow. Its metabolism is closely influenced by vitamin D, Parathormone and Calcitonin

Where do we find it?

There are several sources of calcium available to our horses, especially alfalfa and fresh forage, but a good amount is also found in sugar beet. Its absorption occurs in the small intestine and its elimination occurs through urine, faeces and sweat.

Calcium deficiencies and excesses in the ration

Calcium deficiencies can cause growth delays and deformities in foals, in adults they are rare and shown with lameness, fractures or simply poor athletic performance. Equally, infrequent event is the acute deficiency shown with neurological problems, tremors, decreased intestinal motility and may result in dystocia or placental retention in mares.

The effects due to excessive calcium intake have not been established definitively, it seems that the horse well bears a calcium intake even 5 times higher than necessary. However, some studies indicate that high levels of this macro element in the ration may interfere with the absorption of minerals such as iron, zinc and copper. Besides, an extremely high intake of calcium has been implicated in orthopaedic developmental disorders.

Pay attention to the losses of Calcium

If the outside temperature is high, the amounts of Calcium lost through sweat can be important. Replenishing losses through the use of mineral feed is absolutely recommended. Reidral CY provides Calcium in the form of calcium gluconate and replenishes calcium ions dissipated by sweating, as well as other electrolytes.



Phosphorus, like calcium, is involved in bone metabolism, 85%, in fact, is stored in the skeletal apparatus and performs several functions, including maintaining the pH at the blood level, is a constituent of enzymes, phospholipids, proteins and nucleic acids (DNA and RNA) and forms energy links (ADP and ATP).

Where do we find it?

Phosphorus is partly found in hay and is much more bioavailable than in cereals. Its absorption always occurs in the small intestine and is easier than that of Calcium, even if it is variable according to the age of the horse. Excess excretion occurs by the kidney.

Phosphorus deficiencies and excesses in the ration

Phosphorus deficiencies are really infrequent and manifest with reduced density and bone fragility. The excess of phosphorus is when the horse is fed with high volumes of cereals that represent 50% of the ration. This results in a reduction in calcium absorption and its consequent deficiency. The organism, to compensate for this deficit, demobilizes calcium from the bone that is replaced by fibrous tissue.

Calcium Phosphorus ratio – Ca/p

The Ca/P ratio is very important because, as we have seen, the two macro elements are closely linked to each other. The calcium intake must always be higher than that of phosphorus. The minimum ratio between the two elements must be 1:1, although it is advisable not to drop below 2:1, especially at certain times of growth.

A cereal-rich diet unbalances this ratio towards phosphorus. In the grains also, especially in the bran, there is phytic acid, an anti-nutritional factor that chelates both microelements and macro elements such as calcium and magnesium, making it difficult to absorb them.

As for the hay, the ones with the best Ca/P ratio are definitely those of alfalfa. This forage has a higher percentage of digestible nutrients than any other hay, it is in fact rich in proteins, vitamins (A, D, E, K, B). In addition, calcium and magnesium are significantly more absorbable in the alfalfa than hay of graminaceous.

Calcium and Phosphorus in sport horses

To understand the importance of the Ca/P ratio in athlete, it is useful to give a practical example: in a sports horse, a ration consisting of hay and oats provides only 40% and 70% of the demands of Calcium and Phosphorus. For this reason it is recommended to use a complementary feed to support diets based only on hay and cereals in which these two macro elements are present in a balanced and easily absorbable form. You can use a balancer as Training, studied properly to cover the needs of growing horses that are preparing to start a competitive career. This complementary feed, in addition to calcium and phosphorus in optimal quantities for this stage, also provides noble protein (rich in essential amino acids), vitamins, trace elements and glucosamine and MSM to support the joint system.


Many people ignore that the intense physical exercise increases the mineral requirements of the adult horse, the constant remodeling of the bone takes place in all sports horses of all ages and this implies the need for Calcium and Phosphorus in a balanced way throughout life.

Several studies conducted on horses used in galloping races have shown that over 40% showed calcium deficiencies due to a high concentration of cereals in the diet during the period of competitions. It is wrongly thought that Calcium and Phosphorus are important only in the development phase, but several works have shown the importance of these elements in the sport horse of all ages and all disciplines.

Requirements of Calcium and Phosphorus

Surely the first year of age of the horse is identified as a fundamental period for the assumption of these two elements because the skeleton must consolidate. Therefore, it is necessary to provide mineral feed with a correct Ca/P intake, to avoid negative consequences on the bone system. The following table shows the needs in Calcium and Phosphorus at different ages and different stages of the reproductive cycle for a horse of about 500 kg of body weight:

Horse in mantainance2014
Horse in hard training4029
Colt and fillies37-4020-22
Pregnant mare until 6th month2014
Pregnant mare until 9th-11th month3626
Lactating mare6038

From the above data, it can be seen that in the foal the Ca/P ratio must be 2:1. Osteo Foal is a mineral feed that provides Calcium and Phosphorus in balanced quantities to meet the correct needs of the growing foal. Osteo Foal also contains other elements such as iron, cobalt, copper and zinc, essential amino acids and vitamins essential for development.


If you have any doubts about the correct calcium and phosphorus intake in the diet of your horse or if you are unsure about other aspects of the ration, ask your veterinarian or an expert in equine nutrition for advice. Equiplanet puts at your disposal its team to assist you in the best feed management of your horse or stable, write to info@equiplanet.it.


  • An examination of the calcium and phosphorus nutrition of thoroughbred racehorses. Caple IW, 1982
  • Potential of alfalfa as a source of calcium for calcium deficient horses. Cuddeford D, 1990
  • Assessment of the calcium and phosphorus nutrition in horses by analysis of urine. Caple IW, 1982
  • Disorders of calcium and phosphate metabolism in horses, Toribio RE 2011
  • Providing Dietary Calcium and Phosphorus to Horses, Peter Huntington KER 2011
  • Effects of phytase supplementation in mature horses fed alfalfa hay and pelleted concentrate diets. Lavin TE, 2013
  • Problems In Equine Nutrition, Joe D. Pagan, 2004