Nonlinear growth and body nutrient deposition models in Japanese quail (coturnix japonica) from 1-36 d

Growth curves are key tools for developing and evaluating new feeding programs. This study aimed to evaluate five nonlinear models (Brody, von Bertalanffy, Gompertz, Logistic, and Richards) to describe growth and understand nutrient deposition dynamics in female Japanese quail from 1 to 36 d of age. A total of 225 quail were reared with ad libitum access to feed and water. Every three d, quail were weighed, and one group was fasted for 12 h and slaughtered to determine body protein, fat, and ash contents. Model accuracy was assessed using R², Akaike (AIC), Bayesian (BIC) information criteria, and the Asymptotic Index (AI), ΔAIC, ΔBIC, and by evaluation of biological plausibility. The Gompertz model best fitted body weight and ash deposition, the Logistic model best described crude protein deposition, and the Richards model was selected for fat deposition. Observed and predicted values showed high agreement, with mean bias within ±0.5 g for all traits except fat (-0.73 g). The predicted maximum daily deposition rates were 4.86 g d^-1 for body weight gain, 1.082 g d^-1 for protein, 1.242 g d^-1 for crude fat, and 0.162 g d^-1 for crude ash. Curve overlap indicated the highest growth rate at 16 d, the peak of protein deposition at 18 d, and continuous fat deposition until 35 d. These findings suggest that current feeding programs should be divided into three phases: 1-18, 19-29, and 30-36 d, optimizing nutrient use, growth efficiency, and productive longevity.