Protein and energy requirements of animals treated with beta-adrenergic agonists: a discussion

Much recent work has established the efficacy of certain beta-adrenergic agonists in promoting muscle growth. These compounds also lower the deposition of body lipid. Establishing whether treatment of animals with beta-adrenergic agonists alters their metabolism in ways that affect the efficiency of nutrient use will become important if these compounds are to find a place in animal production. Currently the biological basis of amino acid and energy requirements is being reexamined; this paper discusses whether we have sufficient information to conclude that the current dietary recommendations are appropriate for animals receiving beta-adrenergic agonists. When dietary protein is not a primary nutritional limitation to the rate of protein deposition, beta-adrenergic agonists should increase the efficiency with which the existing protein intake is used in growth. Alternatively, diets that supply a higher essential/nonessential amino acid ratio might be desirable. Whether additional nonprotein energy should be fed to these animals remains an open question. On one hand, the compounds increase energy expenditure and probably increase the maintenance energy needs of the recipient animals; on the other, feeding diets of higher energy density may lead to the resumption of undesirably high rates of fat deposition.