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Ohio State University Extension


Feeding Horses

Agriculture and Natural Resources
Clif Little, Extension Educator, Agriculture and Natural Resources, Guernsey County

Adequate equine nutrition is essential to the health and the performance of the working horse. However, equine nutrition is shrouded with myths about feed additives, while horse owners search for the truth. This fact sheet provides horse owners with one method of balancing equine rations. Forage is used as a major feed source and is evaluated for its ability to meet a horse's nutritional requirements when fed alone or in combination with each of two different grain supplements. This fact sheet also evaluates the ability of the two different grain concentrates to meet specific nutritional needs. Each of these grain supplements is also evaluated for its ability to provide essential vitamins and minerals. This fact sheet assumes that the reader is an experienced horseperson who has a basic knowledge of equine nutrition, which is provided in Horse Nutrition, Ohio State University Extension Bulletin 762, available at Throughout the fact sheet, basic feeding guidelines are provided.

Comparing Two Rations

Let's compare two different rations which a horse owner is considering. We will compare each diet to the requirements for a three-year-old working horse weighing 900 lbs.; this is an animal that is still growing and that will have a mature weight of 1,000 lbs. (See Table 1). First write out the diet (see Mix No. 1 below) and compare it to the horse's requirements.

Mix No. 1
Diet Concentration Dry Matter Basis Digestible Energy (DE) (megacalories per pound) Mcal/lb. Crude Protein (CP) % Calcium % Phosphorus %
Hay (See forage analysis below) 1.07 15.4 0.94 0.41
Grain (See feed tag below) 1.44 12.0 0.75 0.40
Soybean Meal 1.69 25.0 1.20 0.60
Horse's Requirements (See Table 1 below) 1.29 11.4 0.35 0.25

Horses require forage (pasture or hay) to maintain normal digestive function and to satisfy the need to chew. To feed as much hay as possible, we need to compare the nutrient concentration of the hay to what is required for the horse. When we do this, we learn that the hay is deficient in energy. Next we substitute grain for some of the hay in order to raise the energy content of what we are feeding. It is important to remember that the recommendations for energy vary a great deal, depending on the amount of work (hours duration as well as intensity) that the horse is doing. If horses carry excess body condition, simply decrease the grain and increase the hay portion of the ration. If additional body condition is desired, grain mixtures with higher concentrations of fat may be considered.

To determine the substitution value of 1 unit of grain for 1 unit of hay, we subtract the megacalories of digestible energy per pound in one unit of hay from that of the feed mix:

1.44 megacalories/lb. digestible energy (DE) in the feed mix
1.07 megacalories DE/lb. in one unit of hay
= 0.37 Mcal/lb DE (This is the substitution value.)

Next we determine the percent grain to substitute for hay. The deficiency in an all-hay diet would be:

1.29 Mcal required for the horse
1.07 Mcal in hay
= 0.22 Mcal DE deficiency

0.22 DE deficiency ÷ 0.37 substitution value of grain for hay = 0.59

The diet now becomes 59 percent grain mixture and 41 percent hay. Next, we compare this diet with the horse's requirements:

  Dry Matter % DE (Mcal/lb.) Protein (%)
Dietary Requirement 100 1.29 11.4
Hay 41.0 0.44 6.3
Grain Mix 59.0 0.85 7.1
Total 100 1.29 13.4

The diet is adequate in energy and protein; therefore, there is no nutritional reason to feed soybean meal. However, a slight amount of protein supplement added to the grain may encourage the horse to eat more feed. There may be cheaper alternatives to encourage feed consumption.

Let's look at Mix No. 2 (below).

Mix No. 2
Diet Concentration Dry Matter Basis Digestible Energy (DE) (megacalories per pound) Mcal/lb. Crude Protein (CP) % Calcium % Phosphorus %
Hay (from forage analysis) 1.07 15.4 0.94 0.41
Pelleted Grain (from feed tag) 1.50 12.0 0.75 0.85
Horse's Requirements (See Table 1 below) 1.29 11.4 0.35 0.25

The hay is once again deficient in energy. So we need to substitute grain for hay to raise the energy.

1.50 Mcal/lb DE of grain
1.07 Mcal/lb DE of hay
= 0.43 Mcal/lb DE substitution value

An all hay diet would be deficient by:

1.29 Mcal required for the horse
1.07 Mcal in hay
= 0.22 Mcal/lb DE deficiency

0.22 DE deficiency ÷ 0.43 substitution value of grain for hay = 0.51

The diet now becomes 51 percent grain mixture and 49 percent hay. Comparing this diet to the requirement:

  Dry Matter % DE (Mcal/lb.) Protein (%)
Dietary Requirement 100 1.29 11.4
Hay 49.0 0.52 7.5
Pelleted Grain 51.0 0.77 6.1
Total 100 1.29 13.6

Again, this diet is also adequate in protein and energy.

Calcium and Phosphorus Requirements

Now let's look at the calcium and phosphorus contents of these two diets and compare them to the horse's requirements.

Mix No. 1 — Calcium and Phosphorus Requirements, Dry Matter Basis Mix No. 2 — Calcium and Phosphorus Requirements, Dry Matter Basis
  DM % Ca % P %   DM % Ca % P %
Requirements 100.0 0.35 0.25 Requirements 100.0 0.35 0.25
Hay 49.0 0.461 0.201 Hay 49.0 0.461 0.201
Grain Mix 59.0 0.44 0.24 Pelleted Grain 51.0 0.38 0.43
Total 100.0 0.83 0.40 Total 100.0 0.84 0.63
Difference from Requirements   +0.48 +0.15 Difference from Requirements   +0.49 +0.38
1Values obtained by multiplying content in feed by percent of feeds in diet. 1Values obtained by multiplying content in feed by percent of feeds in diet.

Both of these diets are adequate in calcium and phosphorus. Calcium has been fed at more than five times the recommended level without detrimental effects to adult horses. However, for safety, adult horses should not be fed Ca: P ratios above 6:1, and young (less than one year) horses should not be fed ratios greater than 3:1. When phosphorus intake exceeds calcium intake (i.e., ratios of 1:1 or less), calcium absorption can be reduced. Therefore, feeding diets with more phosphorus than calcium is never recommended. Supplementation of calcium and phosphorus is best provided by top-dressing on the grain ration and should be provided according to the manufacturer's recommendations.

Converting Dry-Matter Basis to an As-Fed Basis

The last step in formulating the ration is to convert dry-matter (DM) basis to an as-fed basis.

Mix No. 1
  % DM of Feed Parts DM in Diet Parts1 Percent2
Hay 91.9 41.0 44.61 4.5
Grain mix 90.0 59.0 65.5 59.54
Total     110.1 100.1
1Calculated 41.0/0.919 = 44.61           2Calculated 44.61/110.1 = 40.5

The recommended Dry Matter intake for a 900-lb horse with a heavy work intensity is 21.1 lbs/day. Therefore:

0.405 x 21.1 = 8.54 lbs of hay
0.595 x 21.1 = 12.55 lbs of grain
    21.09 lbs/day
Mix No. 2
  % DM of Feed Parts DM in Diet Parts1 Percent2
Hay 91.9 41.0 44.61 4.5
Grain mix 90.0 59.0 65.5 59.54
Total     110.1 100.1
1Calculated 41.0/0.919 = 44.61          2Calculated 44.61/110.1 = 40.5
0.48 x 21.1  = 10.1 lbs of hay
0.52 x 21.1 = 11.0 lbs of grain
    21.1 lbs/day

When we evaluate the amount of each grain mix we will need to feed, the amounts are relatively equal. So what are the cost differences? Are they equal in price? The other consideration is the source of energy and protein. Mix No. 1 lists on the feed tag "animal protein." Mix No. 2 lists all "plant" protein and energy sources. Research has indicated that working horses may perform better when fed plant energy as protein sources. Pelleting will prevent some horses from selectively refusing ingredients. In addition, pelleted feed may be less dusty; it also provides more uniform distribution of minerals and vitamin supplement.

When feeding the concentrate portion of the ration, no more than 0.75 percent of the horse's weight should be fed at one time. For example, if the horse weighs 1,000 pounds, we would feed no more than 7.5 pounds of concentrate at any one feeding. Working horses should be fed at least two times a day at regular intervals. Make any changes in a horse's ration slowly, over a 10- to 14-day period.

Nutrient Requirements of Horses

The nutrient requirements of horses vary with age, stage of production, size, and work. Table 1 lists the nutrient requirements of a 900-lb. heavily working horse that will mature at a weight of 1,000 lbs.

Table 1. The Nutrient Requirements of a 900-lb. Heavily Working Horse That Will Mature at a Weight of 1,000 lbs.
Body Weight = 900 Age = Three Years Old Work Intensity = High
Nutrient Total Percent
Dry Matter Intake 21.1 lb/day 2.35 %
Digestible Energy 27.3 Mcal/day 1.29 %
Crude Protein 1092.0 grams/day 11.40 %
Lysine 38.2 grams/day 0.40 %
Calcium 33.3 grams/day 0.35 %
Phosphorus 23.7 grams/day 0.25 %
Magnesium 12.6 grams/day 0.13 %
Potassium 41.0 grams/day 0.43 %
Sodium 28.7 grams/day 0.30 %
Sulfur 14.4 grams/day 0.15 %
Iron 383.0 mgs/day 18.1 mg/lb
Zinc 383.0 mgs/day 18.1 mg/lb
Copper 95.8 mgs/day 4.5 mg/lb
Manganese 383.0 mgs/day 18.1 mg/lb
Iodine 1.0 mgs/day 0.05 mg/lb
Cobalt 1.0 mgs/day 0.05 mg/lb
Selenium 1.0 mgs/day 0.05 mg/lb
Vitamin A 18,371 IU/day 870.1 IU/lb
Vitamin D 2,873 IU/day 136.1 IU/lb
Vitamin E 766 IU/day 36.3 IU/lb
Source: NRC 1989. Nutrient Requirements of Horses. 5th Ed. National Academy Press, Washington, D.C.

Mineral Content

To evaluate the mineral content of feed further:

Magnesium: By multiplying the percent of diet dry matter in hay times the percent of the mineral in diet dry matter, we can compare what is being supplied to the requirement.


0.41 parts diet dry matter in hay
x 0.42% magnesium in diet dry matter
= 0.17%

Here, the hay alone provides the requirement, which is 0.13%.

Mineral sources of magnesium vary in their absorption rate, which ranges from 40 to 60%. Supplemental magnesium in sources such as magnesium oxide, magnesium sulfate, and magnesium carbonate are absorbed at approximately 70 percent. Magnesium deficiency is most often seen in the spring. Signs include muscle tremors, nervousness, and possibly death. It should be noted that our forage analysis has a potassium content of 2.23 which is slightly high and can further reduce magnesium absorption.

Potassium deficiency is rare in horses. Forages are good sources and can easily meet the requirements of most horses. Good supplement sources include potassium chloride and potassium carbonate. In this case, the forage will provide an excess amount of potassium.

Sodium helps to regulate acid-base balance and fluid movement across the cell membranes. Our feed tags (see pages 7 and 8) do not indicate the percent of sodium supplied. However, the hay will not meet our requirements, and the grain source is most likely low. Horses should have access to iodized or trace-mineralized salt, which should be provided according to the manufacturer's recommendations. Signs of deficiency include decreased skin turgor, a tendency for horses to lick objects, decreased water intake, and chewing.

Sulfur requirements for horses have not been thoroughly established; 0.15 percent organic sulfur usually meets the requirement. The hay source does not totally meet the need of our horse. Grain sources usually compensate for these shortages. Excess sulfur can cause problems for horses. Sulfur-containing water is a significant source of sulfur. Excessively high levels of sulfur depress copper absorption. Sulfur is also found in protein, and high-protein rations contribute large quantities of sulfur.

Iron deficiency for horses is unlikely since the requirement is 18.1 mg/lb. of dry matter. Iron absorption in nonruminants is usually less than 15 percent.

Zinc may be found in most feedstuffs at a level of 15 to 40 mg of zinc/kg. Horses require approximately 40 mg/kg DM or 18.1 mg/lb. dry matter. Our forage concentration is 34 ppm or 34 mg/kg. This level would not meet our animal's needs. Supplemental zinc should be supplied in the mineral mix. Good sources include zinc sulfate, zinc oxide, zinc chelates, and zinc chloride. Zinc is found in most trace-mineralized salt products commercially available.

Copper is essential for proper enzyme function and maintenance of elastic connective tissue. Copper sulfate is a common supplement source for horses. Our forage contains 14 ppm or 14 mg/kg dry matter. Ration Mix No. 1 at 41 parts hay (0.41 x 14) = 5.74 cu/mg/kg DM. Our requirements call for 4.5 mg/lb. So 5.74 mg/kg ÷ 2.2046 (conversion to pounds) = 2.6 mg/lb of copper. Grains can be a significant source of copper. Our feed tag doesn't list the amount of copper, but the amount available will probably meet our requirements. If you want to increase the copper level, a trace-mineralized salt for horses is available through feed companies such as Buckeye Feeds, Land of Lakes, and others. In this case, the molybdenum level of our hay sample is high (10.2 ppm), so copper supplementation would be essential.

Manganese is necessary for cartilage formation. Horses require 18.1 mg/lb DM or 40 mg/kg DM. Our forage provides adequate amounts if that's all we fed. Multiplying by the parts in the mix, for example, 0.41 x 63 = 25.83 ppm manganese. This converts to approximately 11.7 mg/lb DM. The concentration in our feed will likely meet our requirement. High-level trace-mineralized salt is recommended, especially for brood mares and growing horses. Research suggests that limb abnormalities in newborn foals, enlarged joints, and twisted legs, have been associated with manganese deficiency. As with all minerals, soil pH effects the absorption of manganese in forage plants.

Iodine is essential for proper functioning of the thyroid gland, which regulates metabolism. Iodine supplementation can be done by simply feeding iodized salt. Signs of deficiency in foals include an enlarged area near the trachea called a goiter. The requirement for our horse is 0.05 mg/lb DM or 0.11 mg/kg or ppm. The concentration of iodine in our forage and grain is not provided. Most alfalfa hay contains 0.15 mg/kg. If this is true, then 0.41 x 0.15 = 0.06 mg/kg, which would not meet the horse's needs. Some grains are significant sources of iodine; however, we should supplement through the use of trace-mineralized salt.

Cobalt is part of the vitamin B12 molecule. B12 deficiency has not been found in horses. Likewise, there is no evidence of toxicity in any species.

Selenium concentration in feed is influenced by variations in soil selenium content and pH. Absorption in nonruminants is 77 percent in contrast to 29 percent for ruminants. The FDA has established a limit of 0.3 mg/kg of dry matter for selenium supplementation in cattle, sheep, and swine feeds. Selenium supplementation in equine feeds is restricted only by industry practices. The minimum requirement for horses is 0.1 ppm of the diet. The lethal dose necessary to kill 50 percent of a population of horses is 3.3 mg/kg of a horse's body weight. Low levels of selenium result in weak foals, impaired movement, and difficulty suckling. Supplementation is usually provided in a mineral mixture, complete feed, or trace-mineralized salt.

Vitamin A is important in vision, reproduction, maintenance of epithelial cells, and bone growth. Vitamin A is derived from feed through the conversion of dietary carotene to Vitamin A in the wall of the small intestine. Alfalfa hay is a good source of Vitamin A. Deficiency is often seen as night blindness, impaired conception, elevated cerebrospinal fluid pressure, and convulsive seizures. Feeding too much Vitamin A can cause severe health problems as well. Alfalfa hay contains 20,000 to 55,000 IU/kg DM of Vitamin A. Fresh forage is also a good source of Vitamin A. Our grain sources in Mixes No. 1 and 2 would provide more than adequate levels of Vitamin A. The pelleted feed, however, has twice as much as our ground feed and is within safe limits. When green forages are provided, supplementation of Vitamin A is most likely not needed.

Vitamin D results from ultraviolet irradiation of ergosterol, which is synthesized in plants. Living plants are unaffected by the irradiation, presumably because chlorophyll screens out the wave length of light. Vitamin D is found in plants after they have been cut and exposed to sunlight. Horses synthesize Vitamin D through exposure to sunlight. A deficiency of Vitamin D is unlikely when animals have exposure to sunlight.

Vitamin E and selenium requirements are interrelated. Storage of forages can affect the concentration of Vitamin E. Grinding and storage reduces the concentration of Vitamin E in feeds. Fresh forages are a good source of Vitamin E. We would not expect deficiencies if we feed hay along with a complete feed normally supplemented with Vitamin E.


Feeding good quality hay is an important nutritional practice for horse owners. In fact, horses should consume at least one percent of their body weight (dry-matter basis) in hay or pasture grasses each day. In most cases, the forage is capable of providing all or most of the nutritional requirements of horses. In the case of working horses, energy will probably need to be supplemented in the form of grain concentrates. Feed these concentrates according to body condition.

A forage analysis is a valuable tool in evaluating supplementation of trace minerals and energy. Horses do not digest poor quality forages effectively. Purchase only analyzed forages of high nutritional quality (forages with an acid-detergent-fiber [ADF] level below 45% and a neutral-detergent-fiber [NDF] value below 65%). Once you know the quality of the forage you are feeding, you can better evaluate what feed and trace-mineral supplement best meets your animal's needs.

Hay to be Fed with Both Mix No. 1 and Mix No. 2
Orchard Grass / Alfalfa Analysis Results
Components As Sampled Basis Dry Matter Basis
% Moisture 8.1 ####
% Dry Matter 91.9 ####
% Crude Protein 14.2 15.4
% Adjusted Crude Protein 14.2 15.4
% Soluble Protein   42
% Acid Detergent Fiber 29.1 31.7
% Neutral Detergent Fiber 48.6 52.9
% Crude fat 4.5 4.9
% NSC 15.4 16.8
% TDN 56 61
NEL. (MCAL/LB) 0.60 0.65
NEM. (MCAL/LB) 0.60 0.65
NEG. (MCAL/LB) 0.35 0.38
% Calcium 0.86 0.94
% Phosphorus 0.38 0.41
% Magnesium 0.39 0.42
% Potassium 2.23 2.43
% Sodium 0.050 0.054
PPM Iron 126 137
PPM Zinc 31 34
PPM Copper 13 14
PPM Manganese 58 63
PPM Molybdenum 10.2 11.1
% Sulfur 0.25 0.25
Relative Feed Value   113
% Ash 9.20 10.01
% Degradable Protein   61
Horse DE (Mcal/lb) 0.98 1
Horse TDN (%) 50 54
% Lignin 4.9 5.3
Comments: (1) TDN determined by OSU equation. Net energies determined using 1988 NRC dairy equation. (2) Horse energies conform to the 1989 NRC nutrient requirements of horses.


  • National Research Council. Nutrient Requirements of Horses. NAS-NRC. Washington, D.C. 1989.
  • Ohio State University Extension. Horse Nutrition. Bulletin 762.
  • Pennsylvania State Cooperative Extension. Pasture and Hay for Horses. Agronomy Facts 32.

The author would like to especially thank Dr. Robert Kline, Ohio State University Extension Equine Specialist, and Dr. Jack Cline, OSU Professor Emeritus, Department of Animal Science, for reviewing this document.

Originally posted Jun 2, 2016.