Analysis oT growth oT broilers with restricting and unrestricting initial body weight in Gompertz-Laird model in different environments

The objectives of the present study were twofold. The first objective was to compare the original Gompertz-Laird model with two other versions of the Gompertz-Laird models where the model parameter of the initial body weight (BWo) was restricted in two different ways: 1) BW0 was set to be the mean of the observed initial body weights, 2) BW0 was allowed to vary within an interval of ±3op around the mean of the initial observed body weights. The second objective was to estimate growth curve parameters for live weight of broilers using the selected form of the model, then to investigate the effect of environmental fluctuations on the model parameters.Data were obtained from the 278 broilers that were reared in diverse environments where temperature, sex, and feeding regimes were the factors creating the environmental diversity. Models were compared using coefficients of determination (R2), correlation between the observed and the estimated growth curves (r), residual standard deviation (RSD), and the estimated mature body weight (BWa).The restrictions applied on BW0 did not improve the fitting of Gompertz-Laird model, and resulted in estimating model parameters that are out of the parameter space. The unrestricted form of the Gompertz-Laird model was, however, observed to be suitable for explaining the growth of broilers. Broilers subjected to 21°C reached the age of maximum growth about 3 days later than the broilers subjected to 30°C. The initial specific growth rate (L) and the rate of exponential decay (K) of the initial specific growth rate were lower in 21°C than 30°C. The model parameters of BW0, L, and K were affected by differences in feeding regimes.