Equine mineral needs are among the major concerns of most horse owners, regardless of the type or size of horse involvement. Many articles appear in the popular Press regarding potential mineral benefits for enhanced performance, prevention or curing disease and remedying a host of common production problems. An aura of mysticism has historically surrounded minerals, due to the complex mineral interactions occurring with various body processes and the lack of accurate, controlled research on the horse's mineral needs.

This report is intended to provide the reader with a summary of the known mineral needs of horses and the mineral composition of selected hays and grains. The report briefly identifies the estimated mineral requirements of horses based on recommendations from the National Research Council's Nutrient Requirements of Horses (NRC, 1989).


Estimated Requirements for Different Classes of Horses

Table 1 lists the estimated mineral requirements for various horse classes based on NRC recommendations. The NRC is the scientific body responsible for evaluating research findings and making recommendations for horse nutrient requirements. These recommended mineral concentrations are based on typical diet consumption levels. Mineral concentrations are expressed as a percent (%) of total diet or parts per million (ppm)on a dry matter basis. Parts per million is equilivant to milligrams of mineral per kilogram of diet (mg/kg).


Calcium and Phosphorus

Calcium (Ca) and phosphorus (P) will be discussed together because of the close metabiolic interaction of these minerals. Although active in many body processes, the primary requirement for Ca and P is related to bone development. As such, rations developed for growing horses must have well-defined Ca and P levels. The dietary need is related to growth rate, so current requirement recommendations must be related to daily energy consumption. Weanlings require a relatively large concentration of Ca and P, as compared to other growing horses, due to their rapid bone development. The requirements for both minerals increase in late gestation for fetal development and in lactation to replace losses in milk. The metabolic interaction of Ca and P has long been recognized. Bone structure of horses will be weakened by consuming rations containing more P than Ca. Therefore, it is recommended that rations never contain Ca to P ratios below one. Optimally, it is recommended that rations contain 1.5 to 2 times more Ca than P.


Magnesium

In addition to its role in energy metabolism, magnesium (Mg) is an important skeletal component. Compared with Ca and P, the requirement for Mg is relatively small. During gestation and lactation, horses require slightly higher Mg intake and have denser rations similar to Ca and P. Because large amounts of Mg can be lost through sweat, diets fed to working horses must contain a slightly larger concentration of the mineral. Compared to Ca and P, research evaluating Mg deficiency or toxicity is limited. However, problems related to Mg deficiency and grass tetany in cattle are of less concern in horses. Maximum acceptable concentrations are based on research with other species because specific information has not been reported for horses.


Potassium

Potassium (K) is heavily involved with maintaining proper cellular pH and osmotic environment. Requirements for K are comparable to Ca and P. Like Mg, increased concentrations are recommended for mares in production and working horses.


Sodium

Sodium (Na) and K have similar functions. Like many minerals, the horse's body regulates Na levels by controlling urinary loss. Because of the high Na loss in sweat, rations fed to working horses must contain a larger Na concentration.


Iron

Iron (Fe) is classified as a trace mineral because it, like several other minerals, is needed in small amounts. Although Fe is classified as a trace mineral, it is of major concern in working horses, due to its close association with hemoglobin in the blood oxygen carrying system. As a result, it commonly is oversupplemented. Deficiencies are not a practical problem, although iron toxicities have been reported to cause death.


Zinc

Zinc (Zn) has recently received much research because of its reported relationship in developmental leg disorders. Several studies have been conducted in the last five years to better define the need of Zn for growing horses. Recommended Zn concentrations are the same for all horse classes. Although horses are generally tolerant of Zn excesses, there are reports of developmental leg disorders in horses fed large amounts of the mineral, possibly due to the interaction of Zn and copper.


Copper

Copper (Cu) is another of the trace minerals with many functions in the horse, a major one being cartilage development in growing horses. Deficiencies are associated with developmental bone disorders in growing horses. Maximal tolerable levels have been estimated to be 800 mg/kg diet.


Manganese

Like Cu and Zn, manganese (Mn) is mostly associated with cartilage development in growing horses. Daily requirements are comparable to Zn requirements, although little direct horse research has been reported for this mineral.


Molybdenum

The NRC does not currently list a requirement for molybdenum (Mo). Mo intakes of 1 to 9 ppm have been reported to interfere with Cu utilization in ruminants. Research has shown that horses are tolerant of larger Mo levels, so excesses appear to pose little problem in horses.


Sulfur

The horse's sulfur(S) requirements have not been adequately evaluated such that recommendations can be made. Rations containing high quality protein sources are thought to provide sufficient S in the form of the S-containing amino acids. Sulfur functions in several different ways in the horse's body; one important one is the development of supportive connective tissue. Although ruminants reportediy have developed Cu deficiencies when fed rations high in S, this has not been reported in horses.


Chloride

Chloride (CI) has body functions overlapping Na and K. Though CI requirements have not been established, it is generally accepted that the CI needs are met when feeding enough salt (NaCI) to meet the Na requirements.


Selenium

Selenium (Se) is another mineral that has received popular press attention. Placental irregularities, foal developmental disorders and muscle tetany have been suggested to be related to Se defldencies or excesses. Several U.S areas contain deficient or toxic amounts of Se in the soil, and problems with Se have been studied for many years in all classes of livestock. Maximum tolerable levels are estimated to be 20 times the requirement.


Table 1. Estimated Mineral Requirements for Different Classes of Horses

Estimated Requirements (Dry Matter Basis)
Adapted from National Research Council, Nutrient Requirements of Horses

© 2000 by Healthy Horse Headquarters