NUTRITION
PIH-3
pork industry handbook
PURDUE UNIVERSITY • COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, INDIANA
Dietary Energy for Swine
Authors
Palmer J. Holden, Iowa State University
Gerald C. Shurson, University of Minnesota
James E. Pettigrew, University of Minnesota
Reviewers
Richard C. Ewan, Iowa State University
John P. Hitchcock, University of Tennessee
William G. Luce, Oklahoma State University
Pigs require energy to maintain normal body processes, to grow and to reproduce. Feeds supplying energy are major components of all swine diets, and the quantity of diet voluntarily consumed by pigs is related to its energy content. Carbohydrates from cereal grains are the most abundant energy source in swine diets. Fats and oils contain more energy than carbohydrates per unit weight but are included to a lesser extent. Amino acids, or protein, may serve as an energy source if included in the diets in excess of animals’ requirement for protein synthesis.

The value of a feedstuff is based on several factors: payability (how well the material will be consumed by an animal), availability of energy and the feed’s contribution of other nutrients (protein or amino acids, vitamins, minerals). Should a pork producer buy com, wheat, or oats as a feed ingredient? This depends primarily on the cost of these ingredients and their value as sources of energy and other nutrients for the pig.

Measurement of Energy
To make sound decisions in selecting feed ingredients, it is desirable to have an understanding of the system by which feedstuffs are rated for energy content and the use of these ratings toward meeting the energy requirements for pigs’ growth
and production. The gross energy (GE) of a feed ingredient is defined as the heat produced when a substance is burned. It is expressed as calories per unit weight. A calorie is the amount of heat required to raise the temperature of one gram of water from 14.5 to 15.5 degrees C. A kilocalorie (kcal) is 1,000 calories, and a megacalorie (meal) is a million calories.

Not all of the feed consumed is digested and absorbed. Some energy is lost in the fecal material (Fig. 1). Thus, GE is a poor estimate of energy for the pig. The amount of energy remaining after subtracting the fecal energy loss from total energy intake is designated as digestible energy (DE). The difference between GE and DE may be large. The greater the digestibility of energy (DE/GE) the greater its value as a source of energy to the animal. DE is a more meaningful measure for livestock producers than GE.

Metabolizable energy (ME) is the "usable" energy of a feed for the pig to live and grow and is obtained by subtracting the urinary energy loss from the DE. In most cases, metabolizable energy represents approximately 95% of the digestible energy content, so the conversion from DE to ME can be made easily.
Some energy is released as heat as a result of inefficiencies in the metabolism of the nutrients. This is called the heat incre-

Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. We adhere to the policy that all persons shall have equal opportunity and access to our programs and facilities.