Late vs. Early Enzyme Responses
Bird responses to enzyme product inclusions were mainly observed in the grower phase of the present
study. It is generally expected to observe greater responses to exogenous enzymes in younger animals as endogenous enzymatic activities in the digestive tract are limited, and this can limit efficiency of the digestive tract at the early stages of life (Olukosi et al., 2007b). However, results of the present study did not exactly follow this pattern because there were no effects of enzyme products on ileal digestibility parameters in the starter phase. There were no differences in ileal digestibility of nutrients and energy between the PC and NC diets in the starter phase, and in some cases, digestibility values of the NC diets were even higher than the PC diets. The reasons for these observations are not clear; however, this situation might have played a role with respect to the lack of effects of enzyme products in the starter phase.Gracia et al. (2003) reported positive effects of dietary supplementation of α-amylase on nutrient digestibility at d 28 in male broiler chickens fed with corn-soy diets. This can suggest that in some instances, exogenous enzymes may not exert positive effects at early stages of life, and there could still be a possibility for further enhancements in nutrient digestibility at later stages (Gracia et al., 2003). This could be an indication that the digestive tract of broiler chickens might not be completely developed by 28 d of age and nutrient digestibility can still be further enhanced (Gracia et al., 2003). This may, to some extent, explain why enzyme effects were observed in the grower phase of the present
study.