Genetic analysis of Gompertz growth curve parameters in the Japanese quail

1. This study evaluated the genetic variation of growth curve parameters in Japanese quail using nonlinear mixed-effects models based on the Gompertz model.2. Two three-parameter mixed-effects models were fitted to longitudinal body weight data to estimate biologically meaningful parameters: initial weight (W₀), growth rate (k), upper asymptotic weight (A) and inflection point age (T_i). These individual-specific parameter estimates were subjected to genetic analysis using a quadrivariate animal model with appropriate fixed and random effects.3. Results showed a satisfactory model fit (CV(RMSE) ≈6%). Females had greater mature size and later maturation, whereas males showed faster early growth. Heritability estimates were moderate, with the highest value observed for asymptotic weight (h² = 0.35). Genetic correlations indicated important trade-offs between growth rate and final size (r_G(k,A) = -0.46) and a near-complete negative association between k and Ti (r_G = -0.98).4. The k-means clustering analysis distinguished three growth profiles, corresponding to fast-maturing light quails, intermediate birds and slow-growing heavy individuals. These findings demonstrated the utility of growth curve modelling in genetic evaluations and offer pathways for targeted selection strategies in quail breeding programmes.