# A Reassessment of Tryptophan Requirements for Aged Brown Laying Hens Using Amino Acid Biomass

## TL;DR

This study determines the optimal tryptophan intake for aged brown laying hens to improve performance without affecting egg quality.

## Contribution

The study provides updated tryptophan requirements for aged hens using L-Trp biomass and identifies optimal intake for maximum efficiency.

## Key findings

- Optimal tryptophan intake for aged hens ranges from 174.7 to 187 mg/hen per day.
- L-Trp biomass supplementation supports efficient nutrient utilization without impairing performance or egg quality.
- Performance variables were affected by tryptophan levels, but egg quality remained unchanged.

## Abstract

Animal cells cannot synthesize tryptophan (Trp), and metabolic intermediates such as indole-3-pyruvic acid provide only minimal and metabolically insufficient conversion to Trp, reinforcing its classification as an essential amino acid in vertebrates. This study assesses the tryptophan requirements of aged layers using an L-Trp biomass of 60%. A total of 264 hens received eight Trp levels, and performance and egg quality were measured. When significant effects were found, linear–plateau and quadratic–plateau models estimated optimal intake. Trp influenced only performance variables, with ideal intake values ranging from 174.7 to 187 mg/hen per day. Based on Trp intake and its deposition in eggs, the optimal requirement was determined to be 187 mg/hen per day for maximum efficiency.

A reassessment of the Trp requirements for brown laying hens using the Trp biomass source allows an update of the nutritional recommendation, in addition to assessing whether biomass has an adjuvant effect in the diet. This research was carried out with the aim of evaluating the efficiency utilization of Trp and determining the ideal Trp intake for aged brown laying hens using the L-Trp biomass 60%. A completely random design was used, with eight treatments and eleven replicates, totaling 264 hens. The diets were formulated by supplementation technique using one basal diet with 0.112% of digestible Trp, resulting in amino acid levels that ranged from 0.112 to 0.225% of digestible Trp. The variables analyzed were performance and egg quality. When the effect of Trp levels (p ≤ 0.05) was detected, the model’s linear–plateau (LP), quadratic–plateau (QP), and the first intercept of the QP in the plateau of LP were adjusted to determine the ideal Trp intake. The results obtained show an effect of the treatments (p < 0.05) only on the performance variables. The first intercept results obtained were 186.2, 174.7, 182.7, and 182.5 mg/hen per day for egg production, egg mass, feed conversion ratio, and feed efficiency, respectively. Dietary supplementation with L-Trp biomass 60% effectively meets the nutritional requirements of aged brown laying hens, supporting efficient nutrient utilization without impairing productive performance or egg quality.