The biological basis of Maintenance and its relevance to assessing Responses to nutrients

Abstract

Animals exhibit a first priority, or threshold, energy requirement that must be met from dietary intake before there will be a yield of products. When fasted, rested and held in a thermoneutral environment, animals exhibit a basal level of energy expenditure that is supported by oxidation of substrates, principally lipids and amino acids, mobilized from body tissues. It is widely presumed that the maintenance energy requirement is the dietary metabolizable energy (ME) required to meet this first-call basal metabolic rate plus the energy needed to support minimal activity and urinary energy excretion (Agricultural Research Council, 1980); that is maintenance ME provides for energy balance under confined conditions. Questions that immediately arise are: what are the metabolic components of maintenance energy expenditure, what are their quantitative roles, is energy balance achieved by simply meeting basal energy expenditure and do the metabolic components of basal metabolism change with level of intake? These questions will be addressed in the present paper.