Phenylalanine requirement of kittens and the sparing effect of tyrosine

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 X 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.