Quantitative Evaluation of the Threonine, Isoleucine, Valine and Phenylalanine Needs of Adult Swine for Maintenance

Abstract

A completely purified diet containing crystalline L-amino acids as the sole source of dietary nitrogen was used to evaluate the threonine, isoleucine, valine and phenylalanine requirements for maintenance of the nongravid gilt. To determine the requirement for individual amino acids a quadratic regression equation was fitted to the nitrogen balance data and used to determine the amino acid intake corresponding to a nitrogen balance of 1 g/day (maintenance requirement) and zero (nitrogen equilibrium requirement). Expressed as mg/day/kg3/4, requirements for maintenance of 39, 30, 21, and 21 were found for threonine, isoleucine, valine and phenylalanine, respectively. Distinctly negative nitrogen balance resulted from a dietary void of threonine, isoleucine or valine, but a dietary void of phenylalanine (and tyrosine), although causing a reduced nitrogen balance as compared with the complete amino acid diet, did not effect negative nitrogen balance. The excretion of urea plus ammonia in the urine was directly related to the quality of the amino acid pattern fed. The urinary nitrogen differential between a deficient and an adequate level of threonine, isoleucine or valine was represented largely by urea plus ammonia. Whether suboptimal or superoptimal, the concentration of valine in the diet determined the concentration of free valine in the blood plasma.