Estimating requirements of digestible methionine, lysine and threonine in starting period of broiler chicks, using response surface method

Central composite design (CCD; 5 levels and 3 factors) and response surface regression (RSREG) were used to evaluate the response of broiler chicks [average daily gain (ADG), feed conversion ratio (FCR) and feed intake (FI)] to dietary requirements of  lysine (Lys), methionine (Met) and threonine (Thr). A total of 60 battery brooder units of 6 birds each were assigned to 15 diets in 3 replication from 2 to 16 d of age. Analysis of variance showed that the overall effects of of  Lys, Met and Thr had significant effects on ADG, FCR, however only the effect of Thr on FI was significant (p < 0.05). Also, it has shown that the linear and non-linear effects of those amino acids ADG and FCR was significant (p < 0.05). The interaction among those variables on ADG was significant (p < 0.05) but on FCR was not significant. For both ADG and FCR, the goodness of fit in terms of R² corresponding to RSM models showed a substantially moderate (ADG model: R² = 0.51; FCR model: R² = 0.57) to none (FI model: R² = 0.29) accuracy. The results of this study revealed that the platform of  RSM model (for conducting group amino acid requirements) may be used to describe the inter-relationships (or interactions) between multiple amino acid contents and broiler performance to achieve the optimal target (high performance and low cost). In other words, RSM was also employed to optimize multiple variables to predict the best performance conditions with a minimum number of experiments