The visceral organs (liver, digestive tract, heart, and kidney) comprise only 6% of total body weight but consume 50% of the maintenance energy (Ferrell, 1988). The largest single tissue that consumes maintenance energy is muscle (41% of body weight; Ferrell, 1988); however, muscle consumes only 23% of the total energy consumed for maintenance. Muscle tissue use does not greatly add to the maintenance energy requirements of penned animals but could be considerably larger for animals walking, grazing, and processing forage.