Phytase inclusions of 500 and 2000 FTU/kg in maize-based broiler diets impact on growth performance, nutrient utilisation, digestive dynamics of starch, protein (N), sodium and IP₆ phytate degradation in the gizzard and four small intestinal segments

Abstract

The objective was to investigate the effects of 500 and 2000 FTU/kg phytase inclusions in maize–based diets with appropriately reduced nutrient specifications in comparison to a positive control diet. Diets were offered to Ross 308 broiler chickens from 7 to 28 days post-hatch and growth performance, nutrient utilisation parameters, sodium, starch and protein (N) digestibility coefficients were obtained in four small intestinal segments and IP₆ phytate degradation coefficients were determined in the gizzard and in four small intestinal segments. The transition from positive control to negative control diets compromised weight gains, FCR and toe ash by 10.3%, 6.57% and 11.5%, respectively. However, 2000 FTU/kg phytase supplementation completely restored these parameters. At 500 FTU/kg phytase significantly increased starch digestibility coefficients by 12.7% (0.879 versus 0.780) in the distal jejunum and by 4.41% (0.947 versus 0.907) in the proximal ileum and significantly increased starch disappearance rates in all four small intestinal segments. Significant increases in protein (N) digestibility and disappearance rates were limited to the proximal ileum where 500 FTU/kg phytase increased protein (N) digestibility coefficients by 6.08% (0.785 versus 0.740). Phytase, at both inclusions, significantly increased the recovery of sodium in the three anterior small intestinal segments. Interestingly, sodium digestibility coefficients were correlated (P = 0.051 − <0.001) with starch and protein (N) digestibility coefficients in all four small intestinal segments. The greatest IP₆ degradation of 95.5% was observed in the gizzard from 2000 FTU/kg phytase. However, surprisingly high gizzard IP₆ degradation rates were observed in both non-phytase supplemented diets. In contrast, phytate degradation was far more pronounced in the negative control than the positive control diet in four small intestinal segments. This phytate degradation may be to the consequence of an up-regulation of endogenous mucosal phytase activity generated by the phosphorus deficient diet coupled with the lower calcium concentration facilitating mucosal phytase activity. Weight gain was correlated with phytate degradation in the gizzard (r = 0.789; P < 0.001) to a more significant extent than in the four small intestinal segments. Consideration is given to the possibility that phytase may be enhancing intestinal uptakes of glucose via Na⁺-dependent transport systems.