Growth and Utilization of Dietary Nitrogen and Energy in Chicks Fed Excess Phenylalanine or Tyrosine Diets

Abstract

The body weight gain of chicks given 10% protein diets supplemented with varying levels of phenylalanine or tyrosine was depressed as the supplemental level of these amino acids increased.
Foot and eye lesions caused by excessive feeding of tyrosine were observed. Two out of 5 chicks in the 5% tyrosine group, 4 chicks in the 7% tyrosine group and all chicks in the 9% tyrosine group, suffered from foot lesions. One out of 5 chicks in the 7% and 9% tyrosine groups suffered from eye lesions. In spite of severer growth depression, such lesions were not observed in the phenylalanine group. The accumulated substance was removed from the foot of suffering chicks and it contained approximately 40% of tyrosine on N basis. It is suggested that this accumulated substance may be responsible for the foot swelling of chicks with foot lesions.
Growth depressions of chicks given diets with 5% phenylalanine or 5% tyrosine were alleviated as the dietary protein level increased. When dietary protein level was increased to 30%, the body weight gain of chicks in the tyrosine group was equal to that of the control, whereas considerable growth depression (45%) still remained in the phenylalanine group. Foot lesions caused by feeding a 10% protein diet with 5% tyrosine to chicks were completely prevented by increaing the dietary protein level to 20%.