Serum uric acid response curves reveal optimal lysine requirement in quails

This study evaluated the dietary lysine (Lys) requirement for growing Japanese quails (Coturnix coturnix japonica) using serum uric acid (UA) concentration as a metabolic indicator. A total of 375 seven-day-old quail chicks were randomly assigned to 25 pens in a completely randomized design with five dietary treatments (0.94 %, 1.09 %, 1.24 %, 1.39 %, and 1.54 % Lys) and five replicates of 15 birds each. Birds were fed experimental diets from 7 to 21 days of age, with Lys levels adjusted by replacing cornstarch in a wheat-soybean meal-corn gluten meal basal diet. Sinusoidal, Truncated Fourier Series (TFS), and Morgan-Mercer-Flodin (MMF) models were fitted using nonlinear regression to find the best dietary Lys to minimize serum UA. The fitted models revealed a U-shaped dose-response pattern, with the TFS model providing the best fit (R² = 0.993; RMSE = 0.178; AIC = 5.62) and estimating the Lys requirement for minimum serum UA at 1.42 %, corresponding to a predicted UA of 4.71 mg/dL. The Sinusoidal model yielded a similar estimate (1.40 % Lys), while the MMF model predicted a higher requirement (1.54 %). These results demonstrate that nonlinear curve fitting, particularly the TFS model, can accurately define dietary Lys needs in growing Japanese quails based on serum UA minimization.