Phenylalanine and tyrosine requirements of immature beagle dogs.

Experiments were conducted with immature Beagle dogs to determine the dietary requirement for phenylalanine. With purified L-amino acid diets the requirement for this aromatic amino acid to optimize growth, feed efficiency and nitrogen balance was found to be 0.8%. Dietary limitations in the quantity of phenylalanine resulted in an increase in plasma and urinary urea. Breakpoint analysis of plasma phenylalanine concentrations also indicated a dietary requirement of 0.8%. The present data indicate that the dietary requirement for phenylalanine can be met by supplying approximately 195 mg per 100 kcal metabolizable energy or 518 mg per kilogram body weight per day. In a separate study, tyrosine was found to meet approximately 46% of the phenylalanine requirement of the immature dog. Consumption of diets containing tyrosine in the presence of optimal phenylalanine did not further stimulate growth, feed efficiency or nitrogen balance.