Abstract: 【Objective】 Research on quantificationally describing the model of body weight growth of native Muscovy ducks was carried out. 【Method】 Four body weight growth models were designed using Richards growth function, including 2-level nonlinear mixed effect model considering individual and gender (ModelⅠ), 2-level nonlinear mixed effect model considering individual and gender with autoregressive correlation structure (Model Ⅱ), 1-level nonlinear mixed effect model considering individual (Model Ⅲ), and 0-level nonlinear fixed effect model ignoring individual and gender (Model Ⅳ), to describe the growth characters of individual and population of Muscovy ducks. Information criteria，error variance, average measured and fitted values at different ages, and estimates obtained by fitting the models and growth parameters were compared. 【Result】 The results showed that Model Ⅱ had the best effect overall fit. It was estimated by the model that the birth weight, the mature weight, and the inflexion point age, the body weight and the absolute growth rate at maximum growth rate of male and female native Muscovy ducks were 40 g, 3 504 g, 43 d, 1 523 g, and 65 g•d-1, and 40 g, 2 209 g, 36 d, 977 g, and 45 g•d-1, respectively. 【Conclusion】 Multilevel Richards nonlinear mixed effect model considering individual and gender with autoregressive correlation structure was the best growth model for fitting the body growth of male or female native Muscovy ducks.

Key words: multilevel nonlinear mixed effect model, body growth, Muscovy ducks, evaluation