Work

Requirement of phenylalanine and phenylalanine + tyrosine in broiler chickens fed purified amino acid diets and assessment of phenylalanine as a source of tyrosine

Year: 2026

Type: article

Abstract: ABSTRACT There is a paucity of information on the efficacy of Phe as a source of Tyr in chickens, a question that must be considered when expressing requirements for Phe and Tyr jointly (i.e. Phe + Tyr). The objectives of these experiments were to establish Phe and Phe + Tyr dose-response relationships in male Cobb 500 broilers using purified amino acid diets and to assess the efficacy of Phe as a source of Tyr. In Experiment I, Phe + Tyr requirement estimates were determined in diets devoid of Tyr. Dietary treatments were created by supplementing L-Phe in graded increments of 0.10% to achieve a range of 0.50 to 1.20% Phe. In Experiment II, Phe requirement estimates were determined using diets that contained excess Tyr (0.60%). Dietary treatments were created by supplementing L-Phe in graded increments of 0.10% to achieve a range of 0.20 to 0.90% Phe. In Experiment III, the efficacy of Phe as a source of Tyr was determined using a slope-ratio bioassay. Seven dietary treatments were created by supplementing 0.06, 0.12, and 0.18% of either L-Phe or L-Tyr to a purified basal diet that was devoid of Tyr and contained 0.60% Phe. There were 5 replicate pens of 5 male broilers per treatment in each experiment. In Experiments I and II, there was a quadratic effect of Phe on BW gain and gain:feed ( P < 0.05). Linear one-slope broken-line regression analysis for gain:feed yielded an estimated Phe + Tyr requirement of 0.93% (R 2 = 0.96) in Experiment I and a Phe requirement of 0.44% (R 2 = 0.96) in Experiment II. In Experiment III, BW gain increased linearly in response to supplementation of both L-Phe and L-Tyr ( P < 0.05). The estimated efficiency of L-Phe conversion to L-Tyr using multiple linear regression of BW gain on total Phe + Tyr intake ranged from 96.5 to 97.9% on a weight and molar basis. In conclusion, modern broilers can efficiently utilize Phe as a source of Tyr.

Source: Poultry Science

DOI: 10.1016/j.psj.2026.107901