Valuation of Energy and Protein Requirements for Horses
Author: Neeti Lakhani
Horses can use hay and other roughages as nutrient sources much more efficiently than other nonruminants such as poultry or pigs, but less than ruminants. A source of roughage should comprise at least 50% of the total equine ration by weight. Current recommendations are that horses receive at least 1.5%–2% of their body weight in forage or forage substitutes such as hay cubes or other high-fiber source daily. The average maximum daily dry matter intake is 2.5%–3% body wt therefore, forage or forage substitutes should be the major components of an equine ration. The main sites of fermentation in horses are in the cecum and large colons, where products of microbial fermentation, such as volatile fatty acids, amino acids, and vitamins, are also absorbed. Microbial fermentation also occurs in the stomach and small intestine to lesser degrees, depending on the type of feed. Enzymatic digestion of carbohydrates, protein, and fats occurs only in the duodenum and jejunum. Any of these nutrient sources that escape small-intestinal digestion are passed on for microbial degradation in the large intestine, where their fermentation will alter pH and microbial activity.
Eighty percent of the horse’s fat-free, moisture-free body composition is protein. Protein is a predominant component of blood, muscles, organs and enzymes and it is a critical part of the horse’s diet throughout its life. The age and use of the horse are the most important considerations in determining protein requirements. In addition, other important factors concerning protein which should be evaluated when selecting a ration for a particular phase of a horse’s life are the digestibility of the protein, the amino acid content of the protein, and the protein to energy ratio (PER) of the ration.
Energy requirements may be classified into those needed for maintenance, growth, pregnancy, lactation, and work. However, the need for energy differs considerably among individuals; some horses require much greater amounts of feed than others (“hard keepers”), and others are much more efficient at feed digestion/utilization (“easy keepers”). Digestibility of feedstuffs also often differs significantly from published values. Therefore, the caloric recommendations provided should be considered only a starting point to determine the actual energy needs of a given horse.
Maintenance: For maintenance of body weight and to support normal activity, the daily digestible energy (DE) requirement (in Mcal) of the nonworking adult horse in good body condition is estimated to be on average 33.3 kcal/kg body wt, with a minimum requirement of 30.3 kcal/kg for easy keepers or draft types and 36.3 kcal/kg for hard keeper adult horses. For obese or emaciated horses, the estimated ideal body weight in kg should be used in the equation rather than current body weight. For weight gain, it is estimated that 1 unit of change in body condition score takes 16–20 kg body wt gain and that each kg of gain requires 20 Mcal DE above maintenance requirements. Caloric intake in obese horses should not be restricted severely for prolonged periods of time because of the risk of hyperlipidemia.
Cold weather increases the energy requirement by 0.00082 Mcal DE/kg body wt for each degree Celsius drop below the lower critical temperature (LCT) of the animal.
Growth: For growth, the daily DE requirement of light horse breeds is estimated to be maintenance DE Mcal/day = (56.5X–0.145)/1,000 times body wt in kg plus the caloric requirements for growth = (1.99 + 1.21X – (0.021X2) × ADG, using the above equation(s) for the maintenance DE, and X as the age in months and ADG as the desired average daily gain in kg. Warmblood, draft, and draft-cross breeds may require 10%–20% less than calculated by the equations above to sustain rapid growth and avoid obesity.
Pregnancy and Lactation:
During pregnancy, if the mare is not exercised or exposed to extreme weather conditions, maintenance DE intakes are usually adequate until the last 90 days of gestation. Energy requirements during months 9, 10, and 11 of gestation are estimated by multiplying estimated maintenance requirements by 1.11, 1.13, and 1.20, respectively. Voluntary intake of roughage decreases as the fetus gets larger, and it may be necessary to increase the energy density of the ration by using supplemental concentrates in late pregnancy.
To support lactation, the NRC has estimated that 792 kcal of DE/kg of milk produced per day should be added to the increased (36.3 kcal/kg body wt) maintenance needs. Lactating light horses (eg, Thoroughbred, Quarter horses) maintained body weight when fed 28–31 Mcal DE/day. Draft mares may require as much as 43 Mcal/day. However, this recommended level of energy intake has increased body weight gain in lactating pony mares, indicating that it may exceed the needs of some breeds or individuals. The mare's body condition should be evaluated on a regular basis and maintained in the range of 5 to 7 throughout pregnancy and lactation.
Weanling horses require 50 g CP/Mcal DE (NRC, 1989). The lysine content of weanling diets should be at least 2.1 g/Mcal DE/day. Yearling and long yearling horses require 45 g CP/Mcal DE and 1.9 g lysine/Mcal DE/day. Two year olds require 42.5 g CP/Mcal DE/day and 1.7 g lysine/Mcal DE/day. The protein to energy ratio and lysine to energy ratio are only indirectly related to growth rate.
Although some amino acid synthesis and absorption occurs in the cecum and large intestine, it is not sufficient to meet the amino acid needs of growing, working, or lactating horses; therefore, the protein quality of the feed provided to these classes of horses is important. The amino acid balance in alfalfa and other legumes such as soybeans appears to be better than that found in cereal grains or some grass hays. This should be considered when formulating rations, especially for rapidly growing young horses.
Growing horses have a higher need for protein (14%–16% of total ration) than mature horses (8%–10% of total ration). Aged horses (>20 yr old) may require protein intakes equivalent to those for young, growing horses to maintain body condition; however, hepatic and renal function should be assessed before increasing the protein intake of old horses. Fetal growth during the last third of pregnancy increases protein requirements somewhat (10%–11% of total ration), and lactation increases requirements still further (12%–14% of total ration). Work apparently does not significantly increase the protein requirement, provided that the ratio of crude protein to DE in the diet remains constant and the increased energy requirements are met.
The requirement for energy and protein varies during different stages of growth, so the horse should be fed diet according to the energy and protein requirements.
1. NRC. 1989. Nutrient Requirements of Horses. No. 6. (5th ed.). National Academy of Sciences. National Research Council, Wash. D.C.
2. Ott, E.A., R.L. Asquith, and J.P. Feaster. 1981. Lysine supplementation of diets for yearling horses. J. Anim. Sci. 53:1496
3. Ott, E.A. 1988. Protein and amino acid requirements of the young horse. Horse Research Reports, Univ. of Florida, Gainesville. pp. 20-26.
4. Pagan, J.D. 1982. The digestible energy requirements of lactating pony mares. M.S. Thesis, Cornell University, Ithaca, New York.
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