NUTRITION
PIH-3
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Energy for Swine
Authors
Palmer Holden, Iowa State University
Lowell Frobish, USDA-ARS, Washington, D.C.
Reviewers
Bill G. Diggs, Mississippi State University
Herbert M. Barnes, Ohio State University
The value of a feedstuff is based on several factors: acceptability (how well the material will be consumed by an animal), energy availability and as a source of other nutrients (protein, vitamins, minerals). Should a swine producer buy corn or wheat or oats as a feed ingredient? This will depend primarily on the cost of these ingredients and their value as a source of energy for the animal.

The pig requires energy to maintain normal body processes, to grow and to reproduce. Energy is the major component of all swine diets, and the intake of many other nutrients is related to the energy content of the diet. Carbohydrates from cereal grains are the most abundant energy source in swine rations. Fats and oils contain more energy than carbohydrates but are used to a lesser extent. Protein may serve as an energy source only if included in the ration in excess of the animal’s requirement for protein.
Definition 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 their energy content and the value of these ratings toward the pig's growth and
production. The gross energy (GE) of a feed ingredient is defined as the heat produced when a substance is burned and is expressed as calories per unit weight. A calorie is the amount of heat required to raise the temperature of 1 gram of water from 14.5°C. to 15.5°C. A kilocalorie is 1,000 calories, and a megacalorie is 1,000 kilocalories. Since not all of the feed consumed is digested, some energy is lost in the fecal material (Fig. 1). 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 quite large. The greater the digestible energy value (DE/GE) the greater its value as a source of energy to the animal. This is a much more meaningful measure for livestock producers. In the production and excretion of urine additional energy is lost. Digestible energy minus the urinary energy loss is termed metabolizable energy (ME).
In most cases, metabolizable energy represents approximately 95% of the digestible energy content, so the conversion from DE to ME can be made very easily. Metabolizable energy is the “usable" energy of a feed for

Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. G Diesslin, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to its programs and facilities without regard to race, color, sex, religion, national origin, age or handicap