Standard phytase inclusion in maize-based broiler diets enhances digestibility coefficients of starch, amino acids and sodium in four small intestinal segments and digestive dynamics of starch and protein

• Phytase increased starch digestibility coefficients and disappearance rates in two segments.
• Phytase increased digestibilities of sixteen amino acids in four small intestinal segments.
• Phytase increased sodium digestibility coefficients in four small intestinal segments.
• Phytase influences intestinal uptakes of glucose and amino acids.

The effects of the 500 FTU/kg inclusion of Buttiauxella phytase in maize-based broiler diets were investigated where each treatment consisted of eight replicates of six male Ross 308 chicks per cage. Apparent digestibility coefficients of starch, sixteen amino acids and nine minerals in four small intestinal segments were determined in broilers offered P-adequate, maize-based diets at 40 days post-hatch. The disappearance rates of starch and protein (the sum of amino acids) from the four small intestinal segments were calculated and starch:protein disappearance rate ratios deduced in order to assess the effects of phytase on digestive dynamics. Phytase increased starch digestibility coefficients in the proximal jejunum (0.681 versus 0.538; P = 0.001) and distal ileum (0.959 versus 0.936; P = 0.009) and starch disappearance rates in the proximal jejunum (58.0 versus 43.4 g/bird/day; P = 0.004) and proximal ileum (80.8 versus 71.4 g/bird/day; P = 0.036). Phytase significantly increased (P = 0.003 – <0.001) amino acid digestibilities in four small intestinal segments with the most pronounced responses being observed in the proximal jejunum. Average amino acid data indicated that protein digestibility coefficients and disappearance rates were significantly (P = 0.002 – <0.001) increased in the four small intestinal segments. The magnitude of the responses to phytase in the proximal jejunum for both protein digestibility (0.791 versus 0.481; P < 0.001) and protein disappearance (23.77 versus 15.06 g/bird/day; P < 0.001) were substantial. Digestibility coefficients of both Na and P were significantly (P = 0.027 – <0.001) improved in four small intestinal segments by phytase but this did not apply to Ca. Na digestibility coefficients were significantly correlated to those of starch in three small intestinal segments including the proximal jejunum (r = 0.900; P < 0.001) and Na digestibilities were significantly correlated to protein in four small intestinal segments including the proximal ileum (r = 0.862; P < 0.001). Phytase condensed starch:protein disappearance rate ratios (P = 0.015 – <0.001) in the three caudal segments of the small intestine. A multiple linear regression equation (r = 0.936; P < 0.001) indicated that increasing protein disappearance rates from the proximal ileum would be advantageous, whereas, increasing starch disappearance rates would be disadvantageous in terms of 40-day weight gains. Consideration is given to the likelihood that the impact of phytase on Na absorption along the small intestine holds relevance to the intestinal uptakes of glucose and amino acids.