Animal Nutrition Handbook, 2º Revision
by Lee Chiba
Edition: 2nd., 2009 , Auburn University
The animal getting no feed, doing no external work, and yielding any product is still carrying out vital/essential body processes such as respiration, circulation, maintenance of muscular activities, production of internal secretions, etc. Energy expended in the fasting animal is represented by the fasting “heat production,” and can be measure in the respiration calorimeter (or other method of indirect calorimetry).
Under practical conditions, an intake of feed energy enough to balance the “fasting metabolism” is not an adequate “maintenance” value.