Nutrient Requirements and Balancing Rations for Horses

Author: L.A. Lawrence, Extension Animal Scientist, Horses, Virginia Tech

Publication Number 406-473, July 1996

Table of Contents

Introduction
Maintenance
Activity
Feeding Horses
Example of One Method of Balancing Horse Rations

Introduction

Nutritional requirements of horses are composed of two factors -- maintenance needs and activity needs. These requirements are additive and both must be satisfied if the animal is to maintain its body weight and condition or degree of fitness.

Deficiency or over abundance of some nutrients can also limit horse performance or production. Balancing the diet of a horse begins with meeting maintenance requirements.

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Maintenance

The maintenance requirements of a horse are dependent upon its 1) size (body weight, BW), 2) environment, and 3) individual digestive and metabolic efficiency. Maintenance needs include a voluntary exercise factor essential to the animal's well being. Daily requirements, as proposed by the NRC (1989) in the Nutrient Requirements for Horses, for horses with mature weights of 880, 1100, and 1320 lbs. are shown in Table 1, Table 2, Table 3, and Table 4, respectively. Requirements increase in direct proportion to BW.

Individual variation among horses, which may be large, must be considered in applying requirement information to any individual horse. Unlike other livestock, horses have never been selected for feed efficiency or uniformity.

The NRC (1989) has made nutrient requirement calculations for horses easy for those with access to a microcomputer. A computer program calculates the requirements with information based on the age, weight, and activity of the horse. Nutrient Requirements of Horses, including the computer program, can be ordered from National Academy Press, 2101 Constitution Ave., NW, Washington, DC 20418.

1. Energy
Energy requirements of horses are typically measured in Megacalories (Mcal) of digestible energy. Weight change of the animal is the easiest way to evaluate the adequacy of energy intake. Condition scores (see appendix) or weight tapes can be used to determine the body composition and/or weight of the horse. This should be part of routine horse care. Adjusting energy intake 10 to 15% above or below the requirement should result in weight gain or loss. Table 5 can be used to estimate relative intake of forage and concentrate (grain) based on a percentage of body weight. Table 5 indicates that in most situations horses at maintenance will meet energy requirements with forage alone. In fact, forage is the basis of diets for all horses. The relative feeding values of several hays are based on assigning a value of 100 to timothy hay and comparing others to it: timothy -100, alfalfa - 133, orchardgrass - 105, and legume-grass mixtures have values ranging from 115 to 120. Basically, this means the average alfalfa hay has 33% more digestible energy than the typical timothy hay. Digestible energy (DE) is determined by a digestion trial. It is the difference in the energy found in the feed and the energy lost in the feces.

2. Protein
The protein requirement for maintenance is quite low and is generally met by the protein in good quality forage and grain. No protein supplementation is usually needed unless the forage protein levels are less than 8-9%. Excess protein, above the horse's requirement, is an unnecessary expense and is broken down and used for energy but may also be detrimental to athletic performance. For example, German research with endurance horses has shown a negative effect on fluid balance when high protein diets were fed.

3. Minerals
Since sodium levels are below requirements in most feedstuffs, a source of salt should be available to all animals. Free-choice salt containing trace minerals is usually recommended. Exercising horses should consume 1 to 2 ounces of salt per day.

Quality forages will usually provide adequate calcium (Ca) and phosphorus (P) for maintenance. To be safe, forage analysis is good insurance. Calcium and phosphorus ratios are important for horses. Ca:P ratios of 1.5:1 or 2:1 in the total diet are recommended for most classes of horses and should never be below 1:1. The NRC (1989) states that if P is adequate Ca:P ratios can be as high as 5:1 for mature horses. Recent research suggests Ca:P ratios should not be above 2.5 for growing horses. Alfalfa hay can have ratios of up to 15:1. Therefore, horses fed alfalfa or other legume hays may need P supplementation to maintain a proper Ca:P ratio. Grass hay can be low in Ca and P. Supplementation of grass hay diets should be done with equal Ca:P or with more Ca than P. Diets can be balanced by including proper supplementation in the grain portion of the diet. Grains are high in P and low in Ca so they must be appropriately supplemented as needed. Offering a free-choice mineral containing Ca and P may help meet requirements, but horses cannot be counted on to consume needed quantities of supplements. Using oats or other grains to "cut" or add to commercial diets is not recommended because it may alter Ca:P ratios and dilute minerals and vitamins. There are feeds designed to be mixed with oats, and these are more appropriate choices. Trace mineral requirements are usually met by feeding good quality hay and free-choice trace mineral salt. However, there are some deficiencies in Virginia forages that require close attention. Selenium and copper are generally deficient and adequate supplementation is necessary (Table 6).

4. Vitamins
The vitamin needs for maintenance of mature horses will usually be satisfied by high quality fresh forages. Horses receiving hay for extended periods should receive supplemental vitamin A and E. Vitamin A activity is lost in hay during storage and vitamin E values vary considerably among forages. Vitamin D is provided by exposure of horses to sunlight and by sun-cured hays. The B complex vitamins are synthesized in the horse's digestive tract and supplements are not needed for horses consuming maintenance diets. For more information on vitamins, see Table 6.

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Activity

1. Reproduction
During the first eight months of gestation, the nutrient requirements of mares are only slightly above maintenance. Approximately 60% of the weight of the foal is accumulated during the last three months of gestation. Failure to provide adequate levels of nutrients during late gestation will result in reduced foal size and loss of the mare's body tissue. To insure rebreeding, the mare should gain 0.3 to 0.8 lb per day of weight during the last three months of gestation.

Milk production dramatically increases the requirements for many nutrients. The increases in the mare's requirements are directly related to the amount of milk produced and milk production is related to body weight of the mare. The mare produces about 3% of her body weight in milk during the first three months of lactation and 2% during the period from 4 to 6 months. Energy requirements for lactating mares are twice the maintenance requirement. Protein, Ca, and P requirements increase proportionately to the energy requirements during this time of high productivity.

2. Growth
The NRC (1989) recognizes (Table 4) two levels of growth for foals. The requirements reflect increases in almost all nutrients for rapid growth and moderate growth rates. A foal receiving adequate energy and protein may need additional Ca and P for proper bone development. Adequate trace minerals for growth must also be available in the diet. Nutrient balance is very important in growing horses. A crude protein/energy ratio of 50 g/Mcal DE and 45 g/Mcal DE for weanlings and yearlings is an important consideration for growing horses. Lysine is the first limiting amino acid for horses and is required at 0.65% of the diet for weanlings and 0.5% for yearlings. Lysine requirements are best met with a high quality protein oil meal such as soybean meal. Commercial diets balanced for growth are good investments for foals, weanlings, and yearlings.

3. Work
The influence of exercise on the nutritional requirements of the horse is dependent upon the intensity of the work, its duration, and the size of the horse. Exercise increases the energy expenditure of the horse, but it has little effect on other nutrients with the exception of water and electrolytes (sodium, potassium, chloride, and calcium) if excessive sweating occurs.

Table 3 contains the formulas for calculating energy requirements for horses doing light work (Western and English pleasure, bridle path hack, equitation), moderate work (ranch work, roping, cutting, barrel racing, jumping, etc.), and intense work (race training, polo, etc.). Daily work of 1 hour or more at a moderate level usually raises the energy requirement above what can be supplied by forage alone. Water and electrolytes are lost in perspiration. The electrolytes are important for muscle function and fluid balance. Intense work places stress on horses, and vitamin supplementation is probably effective in performance horses. Electrolytes should be mixed in water and offered to the horse; however, clean, fresh water should also always be available to a horse that has been properly cooled down.

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Feeding Horses

Horses evolved as grazers and do best when fed high forage diets. Bulky feeds must be included in the diet to maintain digestive tract function. Roughage requirements can be met by feeding at least 1% of the horse's body weight as forage. In some situations, diets containing only forage may be undesirable and use of concentrates is necessary. Grains have 50-60% more digestible energy than forage and can decrease the bulk in the diet. Vegetable oils and animal fats have 2.25 times the amount of energy per pound than grains. They also can be used in horse diets. However, they may affect energy metabolism and body composition. Fat should not be added at more than 10-15%, by weight, of the total diet and additional vitamin E should be supplemented to horses fed fat.

Formulation of concentrate mixtures depends on the animal's requirements and the portion of the requirements provided by the forage. To determine the portion of the requirement met by hay or pasture, a forage nutrient analysis should be performed by a testing laboratory. Your local county Extension office can recommend a forage testing laboratory. Table 5 shows recommended concentrate to roughage ratios for different classes of horses, Table 7 contains the nutrient contents for the total diet, and Table 8 provides recommended concentrate allowances to be fed with forages. Concentrates fed with alfalfa can be lower in protein, energy, and Ca than those fed with grasses. However, P should be adequate to meet Ca:P ratios. When trying to balance Ca:P, it is important that laboratory analysis for these minerals be used to insure proper supplementation. Calcium and P nutrition requires careful consideration. Calcium availability is 50-75% and P availability is from 25-35% in typical forages. Remember never to get the P higher than the Ca.

Commercially-prepared concentrates are usually balanced for a particular class of horse. Lactating mares, growing horses, and the horse that is working or training hard need to be fed carefully balanced diets. It may be advantageous to use commercial diets for these classes of horses. Commercial diets should be purchased to meet the protein requirements of the particular class of horse being fed. If alfalfa is being fed, choose a supplement balanced to be fed with alfalfa. If grass is being fed, choose a supplement balanced to be fed with grass hay. The crude fiber (CF) content of a grain mix should range between 7-12%; generally, the higher the CF, the lower the energy.

Consistency is a key to good feeding practices. Change individual feeds in the diet slowly over a period of a week. When feeding horses, remember that individual variation is large and the "eye of the master" plays an important role in providing adequate energy.

Feeding Rules

  1. Feed at least twice a day.

  2. Be consistent in the amount and type of feed. If you must change, change only by 1/4 of the amount being fed per day.

  3. Make sure the horse has salt.

  4. Provide a good source of water kept at about 40 degrees F.

  5. Control parasites.

  6. Check the teeth to see if they need floating (filing off the sharp edges).

  7. Regularly monitor the condition (weight) of the horse.

  8. Provide regular exercise.

  9. Don't allow the hot horse free access to water.

  10. Observe the horse every day for general health (temperature, pulse, and respiration, etc.).

Adapted from NRC (1989) and E. A. Ott, Dietary Nutrient Allowances for Horses. 1984 Feedstuffs, Vol. 56, No. 30, P. 72.

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Balancing Rations for Horses

Steps to take in order to balance a ration
  1. Evaluate the weight and condition of the horse to be fed. Determine the horse's weight by using a scale or using an equine weight tape. Horses should be in moderate condition. The best way to evaluate this is by feeling along the ribs. You should not be able to see the ribs, but you should be able to feel them just under the skin with some fat filled in between the ribs.

  2. Determine the class of the horse, i.e. working hunter, pleasure horse, race horse, lactating mare.

  3. Using the weight and class of the horse, locate its nutrient requirements in Table 1, Table 2, Table 3, and Table 4.

  4. Using Table 5, approximate the amount of forage and concentrate or grain needed by the horse.

  5. Determine the forage to be used, then calculate the nutrients provided by the forage using Table 9.

  6. Subtract the nutrients provided by the forage from the requirements. The difference is what must be provided by the concentrate.

  7. Select the appropriate concentrate and feed adequate quantities to meet energy and/or protein needs.

  8. Balance calcium and phosphorus and provide a trace-mineralized salt at .5 to 1% of the diet or free-choice. Provide vitamin supplements as needed (see text).

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Example of One Method of Balancing Horse Rations

  1. Determine weight and condition:

    The horse is mature in moderate condition and weighs 1100 pounds.

  2. Determine the class:

    The horse is in the performance class, doing moderate work, eventing or ranch work.

  3. Locate the horse's nutrient requirements:

    Find the daily nutrient requirements in Table 2. Using the Ration Calculation Form, fill in the requirements from the table.

  4. Determine the amount of forage and concentrate or grain needed to feed the horse.

    Table 5 indicates that the horse needs between 1.0-2.0% of its body weight in forage and between 0.75-1.5% of its weight in grain. Total intake of feed will be between 1.75 and 2.5% of the horse's body weight and 1.5% of the weight should be fed in forage. To calculate 1.5% of the horse's body weight, using ratio and proportion, set up the formula and solve for X: 
    1.5 lb         X lb   
--------  =  ---------
 100 lb       1100 lb

 (100)    =  (1.5) 1100 (approximately)  [cross multiply]

              1650
X         =   ------       [divide by 100]
               100

X         =    16.5 lb forage
    This establishes that if 1.5 lb is 1.5% of 100 lb, then 16.5 X lbs of forage is 1.5% of 1100 lbs of body weight

  5. Determine the forage to be used and its nutrients:

    A decision is made to use sun-cured alfalfa hay at the mid-bloom stage of maturity. Mid bloom is the stage in which half the plants are in bloom. Using Table 9, find the percentages of nutrients contained in the feedstuff. To make the calculation easier, convert pounds to kilograms at this point. The conversion unit is 1 kg = 2.2 lb.

    Again, ratio and proportion can be used to set up a formula to convert 16.5 lb to kg. 

               6.5
X     =   -----     [divide by 2.2]
           2.2

X     =    7.5 kg of alfalfa hay
    Next, set up formulas to calculate percentage of nutrients supplied by 7.5 kg of alfalfa. 
    Digestible Energy of Alfalfa is = 2.07 Mcal/kg

 (2.07 Mcal/kg) x 7.5 kg = 15.52 Mcal

Crude Protein  = 17% = 17 kg crude protein/100 kg alfalfa

        17 kg        X kg
      --------  =  --------
       100 kg       7.5 kg

X (100) = 17 (7.5)     [cross multiply]

            127.5
X       =  -------     [divide by 100]
             100

X       = 1.27 kg crude protein/7.5 kg alfalfa

Conversion of kilograms to grams

1 kg  =  1000 g

1.27 kg (1000)  =  1270 g crude protein/7.5 kg alfalfa
    Lysine, calcium and phosphorus are calculated similar to crude protein.

  6. Determine what nutrients must be supplied by the concentrate:

    That will be the difference between the nutrients provided by the forage and the nutrition requirements. In this example, the difference will be 9.1 Mcal of energy and 3 g of phosphorus.

  7. Select an appropriate concentrate and determine the amount needed.

    Use either a concentrate mixed by a commercial company or a cereal grain such as oats, corn, barley, or a combination. If a commercial product is used, select one that is designed to be fed with alfalfa hay to bring Ca:P ratios in line, thus insuring that proper balance of minerals and vitamins.

    Oats will be used for this example. The Digestible energy of oats is 2.91 Mcal/kg. To calculate the amount of oats needed each day, set up the following formula: 

    9.1 Mcal of Digestible energy is needed.

 2.91 Mcal       9.1 Mcal
-----------  =  ----------
   1 kg            X kg

X 2.91   =   9.1 (1)

             9.1
X        =  ------ 
             2.91

X        =  3.13 kg oats

Convert kg to lb

   1 kg         3.13 kg
----------  =  ---------
  2.21 lb         X lb

X (1)   =   3.13 (2.2)

X       =   6.89

X       =   7 lb of oats/day
  8. Balance calcium and phosphorus, and provide a trace-mineralized salt at .5 to 1% of the diet or free-choice plus vitamin supplements as needed (see text).

    Calculate additional nutrients supplied by the oats. Evaluate the Ca and P balance. Both Ca and P requirements are met in this ration. This ratio is considered to be in the safe range for mature horses, but to illustrate how to bring the ratio closer to 2:1, a phosphorus supplement will be added. Using Table 10, choose a supplement that supplies P without Ca. Monosodium phosphate is 25.8% P with no calcium. Calculate how much P is needed to provide a 2:1 ratio. 

     103 g Ca 
----------  =  51.5 g P needed
     2

52.1 g P needed to get 2:1 ratio

28   g P supplied by diet

23.5 g needed to supplement diet

Monosodium phosphate

 25.8 g P           23.5 g P
----------  =  ------------------
  100 g P       X g Monosodium P

X (25.8)    =    23.5 (100)

                 2350
X           =   ------
                 25.8

X           =    91 g Monosodium P

     91 g sodium phosphate

Convert to ounces (1g = 28.3 oz)

  1 oz            X oz
--------   =   ----------
 28.3 g           91 g

X (28.3)   =      91

X          =       3 oz of monosodium phosphate per day

This will provide a 2:1 Ca:P ratio. If a trace-mineral salt mix containing selenium is available and a vitamin supplement is provided, the horse should be receiving a balanced diet.

This example illustrates only one method of balancing rations. There are other methods that can be used for more complex formulations, including computer generated least-cost rations. However, the principles used in this example will be applicable in many situations. Using the text and tables of this publication, many of the typical rations fed to horses can be balanced.

Ration Calculation Form

--------------------------------------------------------------------------------------



     Farm ____________________________________


     Animal Type Mature 1100 lb Working Horse


Season Early Spring
                                            Dig.      Crude
                          Amount/day       Energy    Protein   Lysine    Ca     P
                         kg       lb        Mcal        g         g       g     g
--------------------------------------------------------------------------------------

Requirements                                24.6       984       34      30    21

Provided by forage
   (type) Alfalfa       7.5      16.5

Needed in      
   grain ration

--------------------------------------------------------------------------------------
Grain Ration            Amount/day
  Ingredients          kg        lb
--------------------------------------------------------------------------------------

Oats                    3.1 kg   7          9.1        285	       10       3    10

Salt                   56 g

Vit-Min Premix         56 g

Mono Phos               2.8 g   0.09        0.02                                3.5
--------------------------------------------------------------------------------------

Total for ration       10.7    23.7        24.6       1560      70      103    51.5

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Condition

Condition NeckWhithersLoinTailhead,
Pins &
Hooks		RibsShoulder
1
Poor 		Bone structure easily noticeable. Animal extremely emaciated, no fatty tissue can be felt. Bone structure easily noticeable. Prominent spinous processes. Tailhead and hooks and pins project prominently. Ribs project prominently. Noticeable bone structure on shoulder.
2
Very Thin 		Neck faintly discernible. Animal emaciated. Withers faintly discernible. Slight fat covering over base of spinous processes. Transverse processes of lumbar vertebrae feel rounded. Spinous processes are prominent. Tailhead and hooks and pins are prominent. Ribs prominent. Shoulder faintly discernible.
3
Thin 		Neck accentuated. Withers accentuated. Fat built up about halfway on spinous processes. Transverse processes cannot be left. Tailhead prominent, but individual vertebrae cannot be visually identified. Hook bones appear rounded, but easily discernible. Spinous proccesses easily discernible. Pin bones not distinguishable. Slight fat cover over ribs. Ribs easily discernible. Shoulder accentuated.
4
Moderately Thin 		Neck not obviously thin. Withers not obviously thin. Spinous process (ridge) along back. Tailhead prominence depends on conformation, fat can be felt around it. Hook bones not discernible. Faint outline of ribs discernible. Shoulder not obviously thin.
5
Moderate 		Neck blends smoothly into body. Withers appear rounded over spinous processes. Back is level. Fat around tailhead beginning to feel spongy. Ribs cannot be visually distinguished but can be easily felt. Shoulder blends smoothly into body.
6
Moderate to Fleshy 		Fat beginning to be deposited. Fat beginning to be deposited. May have slight crease down back. Fat around tailhead feels soft. Fat over ribs feels spongy. Fat beginning to be deposited.
7
Fleshy 		Fat deposited along neck. Fat deposited along withers. May have crease down back. Fat around tailhead feels soft. Individual ribs can be felt, but noticeable filling between ribs with fat. Fat deposited behind shoulders.
8
Fat 		Noticeable thickening of neck. Fat deposited along inner buttocks. Area along withers filled with fat. Fat deposited along inner buttoocks. Crease down back. Fat around tailhead very soft. Difficult to palpate ribs. Area behind shoulder filled in flush.
9
Extremely Fat 		Bulging fat. Bulging fat. Obvious crease down back. Bulging fat around tailhead. Fat along inner buttocks may rub together. Flank filled in flush. Patchy fat appearing over ribs. Bulging fat.

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See Figure 1. Condition Score System.

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