Phenylalanine Requirement of Kittens and the Sparing Effect of Tyrosine

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Abstract
Two experiments were conducted to determine the phenylalanine requirement of the kitten and the ability of tyrosine to substitute for phenylalanine in the diet. In both studies purified l-amino acid diets were presented to six male and six female specific-pathogen—free kittens for six experimental periods of 10 d each, according to a 6 × 6 latin square design. In the first experiment, kittens were given tyrosine-free diets with either 4.0, 6.5, 7.5, 8.5, 9.5 or 15.0 g phenylalanine/kg diet. Mean daily weight gain and N retention were maximal at 7.5 g phenylalanine/kg diet. In the second experiment, diets contained 10.0 g tyrosine/kg diet, plus 1.5, 2.5, 3.5, 4.5, 5.5 or 10.0 g phenylalanine/kg diet. Mean daily weight gain and N retention were maximal at 3.5 g phenylalanine/kg diet. This indicates that the dietary phenylalanine requirement of the kitten is 7.5 g phenylalanine/kg diet, and that about half of this requirement may be replaced by tyrosine.