Growth curve of different strains of broiler chickens

This study aimed to identify the nonlinear regression model more adequate to describe and compare the growth curve of four strains of broiler chickens. One hundred birds were used, 13 males and 12 females from each strains. There were tested 13 models of nonlinear regression and after that the best model was used to test the parameters equality and the models identity. The average weight at 77 days of age was 3.017, 2.781, 2.724 and 2.587kg to the strains Hulking, Mixed, Carijó and Naked Neck, respectively. The Quadratic Logarithmic model showed better fit the data from Hulking, Carijó and Mixed strains, according to the mean square and mean absolute deviation tests. To the Naked Neck line the statistical criteria showed as more suitable the Inverse Polynomial model followed by the Quadratic Logarithmic. The males and females growth curves were different between and within the strains. The divergence between the evaluated classes was attributed to the decrease of weight rate, c parameter of Quadratic Logarithmic model. Quadratic Logarithmic model could be used to describe the growth curve of the four strains. The Hulking strain presented the faster and the Naked Neck strain presented the slowest growth. The feed system with the objective of change the growth curve must be adopted by the 35^th day of age, to attend the current legislation and the consumer market.

quadratic logarithmic; body weight; nonlinear regression