An important measure of a horse feed’s value is its energy content. Energy content or energy density determines how much feed must be fed to meet the horse’s energy requirement. How much you need to feed then determines the concentration of all other nutrients in the feed. Diets tend to be formulated initially to meet the energy needs of the horse and then adjusted regarding protein, minerals and vitamins. Therefore, horse feeds cannot be properly formulated without knowledge of their energy contents.
Unfortunately it’s not possible to directly measure the amount of useful energy contained in feed in a single laboratory test. These tests or analytic procedures are readily available to measure other variables such as protein and minerals. Energy is supplied to the horse via its diet, but fundamentally energy is not a nutrient but rather the capacity to do work. Therefore, we are trying to measure the ability or the efficiency of feed energy to be converted to chemical energy or work. The potential energy in a feed is influenced by the type and amount of carbohydrate, protein, and fat that is contained in the feed. It is also influenced by the efficiency of digestion and metabolism of a feed.
Energy content of feed is measured in units called calories. What then is a calorie? In nutrition terms, the word Calorie (with a capital C) is the amount of energy required to raise the temperature of one liter of water by one degree centigrade at sea level. A Calorie is the same as a Kilo-calorie (Kcal) which is actually utilized in analytical procedures. Horse feed calorie contents are usually reported in Megacalories (Mcal) which is 1000 kilocalories.
In the animal feeding industry energy can be reported in four categories: Gross Energy (GE), Digestible Energy (DE), Metabolizable Energy (ME), and Net Energy (NE). Gross Energy is actually the only value that can be truly measured in a laboratory. Gross Energy is the total amount of heat produced from the combustion of that feed. The other energy values are based on calculations from countless years of animal research. For example, Digestible Energy (DE), the value utilized in equine nutrition, is calculated by subtracting the gross energy in the feces from the gross energy consumed by the animal. In other words, the Digestible Energy is the amount of energy an animal consumes minus what is lost in the manure. This is only an estimate of digestible energy as some of the material excreted in the feces does not originate from feed but from cells sloughed off the gastrointestinal tract as the food passes through.
Metabolizable energy is calculated by subtracting the urinary and gaseous losses from DE. Net energy starts with ME and also takes into account numerous variables from energy stored in tissues to heat losses.
Digestible Energy is considered fairly archaic by most other livestock species when describing the energy content of feed. This is in part due to the large differences in how efficiently the Digestible Energy is utilized from different feedstuffs. Therefore DE values should only be viewed as a calculated value not an exact measure.
While there are several equations used to estimate DE we still lack a good means of accurately and easily predicting the energy content of different feeds. The equation shown is commonly used; however, it does not accurately predict the DE content of some high fiber feeds, and feeds that are high in fat. Several other commonly used equine feed ingredients were approximately 40-50 % higher in DE when actually measured in controlled digestion studies compared to predicted values. This inadequacy of the current equation to accurately predict the DE content of feeds higher in digestible fibers and fats becomes very important considering many commercial equine feeds on the market today incorporate high amounts of readily digestible fibers and fat. The most accurate way of measuring DE is to carry out digestion trials for all feeds and feed ingredients. These however are very time consuming and costly to carry out. Research has also shown that digestibility may be affected by individual variation, exercise and diet form. More accurate systems of energy evaluation utilizing net energy have been developed, but have not been placed into widespread use because of a lack of information about NE requirements for various classes of horses and the NE contents of different feedstuffs.
There are no regulatory bodies telling equine feed manufactures which method or equation to use to estimate energy content of feed. This means companies can use whatever system they want to predict DE and this can potentially be very misleading to the end user. A feed could be represented as a low energy feed when in fact it is not.
This inconsistency in standardization and prediction of energy content of feedstuffs undermines the selection of horse feeds based solely on the energy content of the feeds. It also makes it virtually impossible to compare energy contents of feeds between different manufacturers. Therefore DE values should not be relied upon when making decisions about which feed is right for your horse.
Whilst we would like to share our estimates of DE, we feel that it is not in the best interests of the consumers to add this information to our tags. We need to standardize the prediction equations the feed industry as a whole uses to calculate DE, so that the end user can actually compare between companies. We also need to devise more accurate methods of determining energy content of feeds as has been done in other livestock species.
Other balances relating to energy sources in the diet should be considered when selecting feeds for individuals including:
Sufficient carbohydrates to help maintain ample energy without overloading the digestive capacity of the horse or causing metabolic disturbances.
Adequate fat to maintain the required energy without negatively affecting palatability and gastrointestinal function.
Sufficient fiber to maintain normal gut and digestive function and limit behavioral disturbances.
Commonly used formula for calculation of Digestible Energy:
There are several different ways to predict DE content, and this has led to a great deal of confusion about how much DE is actually in a horse feed. The most common method to predict digestible energy uses the chemical composition of the feeds and is described in the following equation recognized by the NRC 2007:
DE x (kcal/kg DM) = 2118 + 12.18 x (%CP) – 9.37 x (%ADF) – 3.83 x (%hemicellulose) + 47.18 x (%fat) + 20.35 x (%nonstructural carbohydrate) – 26.3 x (%ash)
Where hemicellulose = Acid Detergent Fiber (ADF) – Neutral Detergent Fiber (NDF) & Non Structural Carbohydrates (NSC) = (100 - %NDF - %Fat - %Ash - %CP).
Contact your Poulin Grain Feed Specialist to test your hay quality and build a personalized diet for your horse.
www.PoulinGrain.com | 800.334.6731
Sources: National Research Council. Nutrient Requirements of Horses. 6 ed. Washington DC: National Academy Press; 2007.