“…For sheep, the AFRC (1993) recommends a single equation for all categories depending on metabolic body mass (W 3/4 ), but for growing animals, we suggested a correction based on the ME concentration of the diet. However, the energy requirement for maintenance is taken as the oxygen consumption of the body, in which half of these needs is used by the walls of the gastrointestinal tract and liver for the absorption and metabolism of the digested nutrients, one third through the skin, kidneys, and nervous tissue and the remainder for basic muscle activities (Seal and Reynolds, 1993;Oliveira et al, 2013). Variations in the activity levels of these tissues, depending on the genotype, age, physiological status, planes of nutrition, urea secretion, and environmental conditions, modify the energy requirements for maintenance, as observed in this study.…”