WITHDRAWN: Effects of dietary energy and protein levels on growth curve parameters of Khazak native chickens

Abstract

This study was conducted to evaluate the effect of dietary energy (ME) and protein (CP) on growth parameters and absolute growth rates in the different ages of the Khazak chicks. A total of 360 one-day-old Khazak chicks were obtained from a local hatchery and in a 3×3 factorial experiment with completely randomized design, chicks were randomly allocated to experimental diets including 2,600, 2,800, and 3,000 kcal of ME/kg, and each containing 17, 19, and 21% CP from 7 to 98 days of age. Four growth model (Gompertz, Logistic, Lopez, and Richards) were fitted on weekly body weight data and the best model were selected by the goodness of fit criteria. Growth curve parameters were predicted for all chicks using the best model and other parameters including age (Ti) and weight (Wi) at the inflection point and absolute growth rate (AGR) in different ages were calculated from growth curve parameters. All parameters were analyzed using the general linear model procedure of SAS. Based on goodness of fit criteria, the Richards model had the lowest Akaike’s Information Criteria (AIC), root mean square error (RMSE), and highest adjusted determination coefficient (R2Adj) than other models and was selected as the best model. The effect of ME was significant on the mature index (k), Wi, Ti, and all AGR parameters (P<0.05) while CP levels were significant on final weight (Wf), Wi, and AGR parameters (P<0.05). The chicks fed with a diet containing 2,600 kcal of ME/kg and 17 % CP had the higher k parameter, and lower Wi, Ti, and AGR than those fed with other diets (P<0.05). Considering that the level of 2,800 kcal of ME/kg and 19 % CP had no significant difference with the level of 3,000 kcal of ME/kg and 21 % CP, therefore diet with 2,800 kcal of ME/kg and 19 % CP was suggested as optimum levels for change the growth curve parameter and having best performance for Khazak chickens during 7 to 98 days of old.