Amino acid supplementation of isolated soybean protein in milk replacers for preruminant lambs

The growth of preruminant calves and lambs fed on milk replacers containing vegetable proteins is generally inferior to that of preruminants given cows' milk. The inferior performance has variously been attributed to an amino acid imbalance, to heat damage in preparation, and to the presence of growth-retarding substances. Soybean products that have been treated to remove, or destroy, growth-retarding substances are now available commercially. An experimental design is described that has been used to determine the order of limiting amino acids in soy protein isolates, and which may also be used to estimate requirements for individual amino acids. The design allows an economy in time and in experimental animals, and gives results that are not significantly different from those determined in classical balance experiments.