Eleven Poll Dorset × Merino crossbred female lambs 4 weeks of age were trained to suck liquid diets from bottles. In three separate experiments liquid diets providing 14° 2 % (expt 1) 10° 6 % (expt 2) or 8°0 % (expt 3) of gross energy as protein and amino acids were fed. Responses in voluntary intake, growth rate and changes in plasma amino acid concentrations were studied when complete or incomplete mixtures of amino acids were added to the liquid diet. These mixtures supplied either: (1) all amino acids in quantities to bring the total of protein plus amino acids to provide more than 20% of dietary gross energy, the amino acids being provided in proportions estimated to meet adequately the lamb's requirements (‘complete’); or (2) as the same total amount of amino acids but with the amino acid supplement devoid of threonine (‘low-threonine’, expts 1 and 2) or isoleucine (‘low isoleucine’, expt 3).
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