Lysine Requirements in Starter‐Phase Japanese Quail ( Coturnix japonica ) Through Dose–Response Modelling: Interactions With Dietary Protein Level

ABSTRACT Background The diet of Japanese quail ( Coturnix japonica ) during the critical post‐hatching period (0–14 days) provides a basis for long‐term productivity, but the exact lysine requirements are not well characterized in modern high‐yield strains. Precision poultry nutrition requires updated amino acid (AA) recommendations that account for interactions between dietary crude protein (CP) and lysine, the reference AA for ideal protein specification. Objectives To determine optimal lysine requirements for growing Japanese quail (0–14 days) at three CP levels (22%, 24%, 26%) using a dose–response method, and to compare linear versus quadratic broken‐line models for estimating lysine thresholds. Methods A fully randomized factorial design used 900 Japanese quail chicks allocated to 15 dietary treatments (3 CP × 5 lysine levels: 0.95%, 1.1%, 1.25%, 1.4 %and 1.55 %). Growth performance, feed efficiency and carcass characteristics were evaluated. Lysine requirements were estimated by linear and quadratic broken‐line regression using the non‐linear least squares (NLIN) procedure in Statistical Analysis System (SAS) software version 9.4. Results Dietary CP and lysine levels significantly ( p < 0.01) affected all growth parameters. Optimal lysine (1.4%) maximized body weight (73.93 g), weight gain (66.50 g) and protein efficiency ratio (PER) (2.70). Significant interactions ( p < 0.05) occurred between CP and lysine for feed intake (FI), feed conversion ratio (FCR) and PER. Lysine requirements for weight gain using the linear broken‐line model were 1.20%, 1.32% and 1.4% for 22%, 24% and 26% CP, respectively, showing superior fit ( R 2 = 66.24%–94.45%) compared to quadratic models. Conclusions Lysine requirements of Japanese quail depend on dietary CP level. The linear broken‐line model is more reliable than the quadratic approach. Producers should use 1.32%–1.42% lysine in starter diets, adjusting according to CP content. Future research should confirm these requirements under commercial production conditions and explore interactions with other key AAs in reduced formulae.