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Feeding the Horse

November 12, 2012

By Peter J Lester

To produce a Triple Crown winner you must first address its nutrition in the womb. The performance of all land dwelling mammals is set in the womb. The formation of their bones, their brain and their constitution is set at conception; set in its DNA.

Energy: In essence, energy is the amount of combustible material in a feed; the portion of the feed that can produce heat. When this commodity is restricted, all other functions are placed on the back burner.

The energy content of a feed may be expressed as the amount of heat produced from the combustible portion of the feed in question and is usually expressed as the Gross Energy of the feed. The chemical portion of the feed will affect the gross energy, where as fats, or lipids as they are often termed, have a higher gross energy per unit (energy potential in Fat = Fat X 2.25) than either carbohydrates or proteins, and the type of carbohydrate, such as the content of cellulose and starch may have a slight effect on the gross energy as well.

Feeds which are composed mostly of minerals are very low in potential energy simply due to the fact that most minerals are virtually incombustible.

When feeds are assessed for horses and cattle, the energy level is usually expressed as the amount of Digestible Energy (DE) present. This equation is based on the amount of apparent digestible energy in the feed and is calculated by subtracting the gross energy in the faeces from the gross energy consumed. Obviously the true DE in the feed can only be calculated if the faecal endogenous losses are known. As these losses are seldom determined, the DE values represent 'apparent DE' not the actual DE.

There are two aspects which impact on the amount of DE in a feed and they are the amount of DE in the feed and the energy-containing components of the feed. The digestible energy content of most feeds for horses has been determined using the foregoing trials. Cattle trials are fairly inaccurate as in the case of the cow, the digestion is performed mainly by biological processes in the rumen. For example, when Lucerne is fed to a ruminating animal such as a cow, it has a digestible value of 2.6 Mcal/kg, but when fed to a horse the DE value falls to 2.43.

The total energy source for horses comes from the consumption of carbohydrates, fat, and protein which can be metabolized. ATP (adenosine triphosphate) is the major source of chemical energy in the animal's cells and is generated from the catabolism of carbohydrates and fats under normal circumstances. The amount of ATP produced is influenced by the animals feeding, its physical condition and the amount of energy potential products in its diet.

For an animal that is not pregnant, lactating or growing or performing work, the amount of energy required is often referred to as the amount required for maintenance. This amount is that required to prevent changes in the total energy contained in the body; the loss of condition.
Three Proposed levels of digestible Energy Intake for Maintenance (Mcal/d) in adult Horses as compared to previous NRC recommendations.

Body Weight



(30.3 Kcal/kg BW)


(33.3 Kcal/kg BW)


(36.3 Kcal/kg BW)




























The amount of energy required for daily exercise (effort) and the amount required for maintenance.

It has been suggested (Doherty et al., 1997) that the energy used in transportation may be similar to the animal walking. Therefore, several hours of transportation could add significantly to the animals total energy requirements.

While no levels were given, it is safe to suggest that a level akin to medium work would be appropriate.

In most cases, energy excess and energy deficiencies can be identified as increase or decrease in weight gain. Because it is difficult for most horse owners to weigh their horses, the use of a body scoring chart would help to determine whether a horse is gaining or losing weight. The following has been suggested (NRC 2009)

(heart girth, cm) X (length, cm)

While TDN is an acceptable measuring stick for total energy, here in this country much of it is made up of excess protein, especially when pasturing animal feeds are being assessed. To a large extent our pasture contain excess protein, (as much as 30 percent) this is taken into account when assessing TDN (TDN% = % crude Protein + % DCF + % DNFE + (% DEE X 2.25)) where DCF = Digestible Crude Fibre) DNFE = Digestible Nitrogen free extract and DEE = Digestible Ether Extract.

Protein: The evidence of too much protein in the horse's diet is excessive urine, as the excess is degraded and results in an increase in urea as urine. This in turn results in an increase in the loss of water from the body, and an increase in the need for the ingestion of water. Recent research has revealed that higher than the level required for body maintenance resulted in lowering the blood pH both at rest and during exercise, a loss of calcium may also result as the lowering of the pH increases the loss of calcium from the blood.

Electrolytes: Racing horses often break bones when high protein diets are fed. The ratio of cations to anions is critical in that they all depend on each other and are said to be synergistic; that is, the joint sum of the total combined effect is greater than the sum of the of the individuals.Any loss of any one element places a greater stress than the loss of the one element individually. In the case of broken bones, copper takes part in the formation of the copper enzyme, amine oxidase.

The ratios of electrolytes are set by nature and are as follows:

For each one part of phosphorus in the diet, there should be:

  • One and one half parts of calcium
  • Three quarters of a part of Magnesium
  • Half a part of sodium
  • And three parts of Potassium

As our pastures contain over 3 percent potassium there is a tendency to believe that the soil is well endowed with this element.This could not be further from the truth. Potassium accumulates due to cation imbalance not because of excesses in the soil profile.

All though the mineral content of the diet constitutes only a minor part by weight, they play a critical role in the animal's health and performance. Most horse health problems can be traced to too much of one product and too little of another. Many minerals play an integral part in the function of vitamins, amino acids and hormones and activator ions. The animal obtains most of these from the feed it ingests.

Water: As water plays such a critical role in any animal's diet, it should NOT contain anything other than H2O. Any supplementary feeding of minerals should be just that, supplementary.

Always check the nitrate levels of all water.

Water must be available to all animals to maintain their fluid balance. The total body weight of the horse has been estimated to be 62 to 68 percent of its live weight. Water balance is achieved by drinking to equalize the intake with loss by perspiration and exercise. Losses also occur in the urine and by defecation. Respiration and skin (cutaneous) loss. Lactating mares lose fluid through their milk.

Temperature extremes such as excessive heat place a greater demand on body fluid and thus the need for pure water. Heat loss is facilitated through the evaporation of water; therefore losses are extensive when heat and exercise coincide.It cannot be over-emphasized that water should be as pure as possible.

Vitamin supplementation may be beneficial especially when feeds are grown on nitrogen boosted soils. When horses are fed on such feeds the conversion of carotenes to true vitamin A is greatly curtailed.

As you can see, the above is not a pretty picture, especially in mineral department and it's all because of the level of potassium. As it stands, the animal is receiving way too much K, 86.67 and it should be receiving only 38.0 there is almost 2 and one third times that required. This is compounded because the levels of the other electrolytes are poorly balanced as well. For example the minimum level for Ca should be 42g and the animals only receiving 5.89g. In fact the whole feeding system is out of phase.

We would need to rebuild the minerals around the most prominent one, in this case, potassium.

For each on part of potassium we need one third parts phosphorus, therefore we need to the 86.67 by three to arrive at the P level. 86.67 divided by three equals 28.89 and we only have 9.9. We already have 9.9, so we will take that away from the level of 28.89 required and we 18.99g of P. as the P level is critical in the ATP side of energy, this level is sure going to play havoc in the animals' performance.

We know we need one part of P for each 1.5 parts of Ca, and this feed requires 18.99g of P to balance the P to K ratio. Now what we have to do is establish how much Ca we will need. To do this we take the 18.99 and multiply that by 1.5 then take away the amount we already have. We have 5.89 and, using the calculation of one part of P to each three parts of K we have established that we are short in this element. Our P level need to be 18.99 and that figure multiplied by 1.5 equals 28.48 and we already have 5.8 so we take that away from the total and we find that we need 22.685g of calcium. As we cannot buy calcium and if we could we could not feed it, we can only buy calcium carbonate; therefore we need to multiply 22.685 by 4 to get enough Ca out of it. 22.685 times 4 equals 90.74g of limestone.

Having established our P level we can now arrive at the level of Mg and Na (Magnesium and Sodium).

We know that there should be three quarters of a part of Mg for each part of P and we have established that the P level needs to 18.99; therefore the Mg level required is ¾ of that level. ¾ of 18.99 equals 14.24 and we already have 7.56 so we need 6.68g of magnesium and the best we can buy is MgOx which has 50 percent Mg, we will need to multiply 6.68 times two to reach our goal. 6.68 times two equals 13.36g of magnesium oxide. The sodium level is way out as well, all due to the excess K level. We know that we should have a half a part of Na for each one part of P, and we have established that the P level needed is 86.67 so we divide the P level by two to establish the Na level. 86.67 divided by two equals 43.335g of salt per day is now required as minimum.

There is another more critical adjunct to high K levels in feeds that may manifest itself as spontaneous heart failure. As this element controls the relaxation phase of all muscles, including the heart, high levels of potassium can result in the heart stopping in the full rest mode, termed potassium inhibition.

The protein energy ratios are out as well and would need attending to.

All electrolytes work in unison and are synergistic in that the sum of the total combined is greater than the sum of the parts. This excess potassium places a load on the other element as the animal has no way of squeezing out the excess before digesting the feed in which it is contained. All other electrolytes must now be balanced or reconstructed to meet the animal's requirements.

As we can see the level of sodium along with all other electrolytes is now low due to the ingestion of the high K. Sodium controls the milk flow. Any lactating mare will have difficulty producing sufficient milk to meet the needs of her offspring, and any gestating mare will have difficulty producing a healthy Triple Crown winning offspring.