Maintenance Requirements for Energy and Amino Acids
The amount of energy and protein intake needed for productive functions is determined after the amount needed for maintenance is computed. The maintenance energy requirement is determined primarily by the animal’s metabolic body size (weight of organs necessary for sustaining life, including the heart, lungs, liver, and digestive tract) and rate of metabolism. Metabolic rate at a particular metabolic body size varies with breed type, physiological state, previous nutritional treatment, activity, environment (temperature, wind velocity, and animal surface area and insulation) and heat gain or loss required to maintain normal body temperature. The combined animal and diet heat production must thus be determined to assess energy balance in a particular environment, requiring the prediction of both metabolizable and net energy.
The amino acid requirements for maintenance are for sloughed protein and net tissue turnover losses, as predicted from metabolic fecal N, urinary N loss, and scurf (from skin) protein.