Abstract
Effect of a phenylalanine (Phe)-free diet on body weight, nitrogen balance and plasma free Phe levels were studied with male White Leghorn aged 2 weeks, 6, 12 and 15 months. Effects of feeding an isoleucine (Ile)- or amino acid-free diet and fasting on plasma amino acid levels in 15-month-old roosters were also studied.
Two-week-old chicks lost appetite for the Phe-free diet and their body weights decreased gradually. Six-month-old cockerels consumed the Phe-free diet completely but could not maintain normal growth rate and positive nitrogen balances. Twelve- and 15-month-old roosters maintained their body weights and nitrogen equilibrium on the Phe-free diet.
Plasma Phe levels of 2-week- and 6-month-old fowls at the 6th hr after the last feeding of the Phe-free diet did not decrease significantly compared to those of the control groups. However, plasma Phe levels of 12- and 15-month-old roosters decreased rapidly within a day on the Phe-free diet. Fasting resulted in a significant increase in plasma amino acid concentrations whereas feeding an Ile- or amino acid-free diet resulted in concentrations of plasma amino acids which were not lower than those observed in the control roosters.
