Effects of phytase inclusions in diets containing ground wheat or 12.5% whole wheat (pre- and post-pellet) and phytase and protease additions, individually and in combination, to diets containing 12.5% pre-pellet whole wheat on the performance of broiler chickens

Abstract

Each of eight dietary treatments was offered to seven replicates (six birds per cage) of male Ross 308 chicks from 7 to 28 days post-hatch. The diets contained 741 g/kg wheat incorporated as ground (3.2 mm hammer-mill screen) wheat or 125 g/kg whole wheat included in diets, either pre- or post-pelleting. In Experiment 1 of the study, ground grain, pre-pellet and post-pellet whole grain diets were offered with and without phytase as a 3 × 2 factorial array of treatments. The effects of dietary treatments on gizzard and pancreas weights, bone mineralisation, excreta dry matter, growth performance, nutrient utilisation, digestibility coefficients and disappearance rates of starch and protein (N) in four small intestinal segments were determined. Post-pellet whole grain addition significantly increased gizzard weight by 12.5% (18.17 versus 16.15 g/kg; P < 0.001). Pre- and post-pellet whole grain additions improved FCR (P < 0.10) by 1.40% and 2.28%, respectively. Exogenous phytase significantly enhanced weight gain by 4.76% (1519 versus 1450 g/bird; P < 0.001) and FCR by 1.99% (1.332 versus 1.359; P < 0.03) irrespective of the context. Significant interactions between grain and phytase treatments were observed for energy utilisation parameters. However, pre- and post-pellet whole grain additions to non-supplemented diets significantly improved AMEn by 0.31 MJ (11.89 versus 11.58 MJ/kg; P < 0.04) and 0.48 MJ (12.06 versus 11.58 MJ/kg; P < 0.001), respectively. Post-pellet whole grain addition to non-supplemented diets significantly improved AME (13.49 versus 12.99 MJ/kg; P < 0.001) and ME:GE ratios (0.79 versus 0.77; P < 0.003). Phytase addition significantly improved AME in ground grain and pre-pellet whole grain diets by 0.43 MJ and 0.30 MJ, respectively. Phytase addition improved AMEn by 0.49 MJ in ground grain diets but this was not significant and otherwise did not influence AMEn. In Experiment 2, phytase and protease, individually and in combination, were included in diets containing 12.5% pre-pellet whole wheat as a 2 × 2 factorial treatment array. There was a significant interaction (P < 0.015) for weight gain following phytase and protease additions to pre-pellet whole grain diets where phytase significantly increased weight gain by 6.91% (1548 versus 1448 g/bird). Protease supplementation alone numerically increased weight gain, but in combination with phytase, numerically decreased weight gain. Phytase improved FCR by 2.15% (1.319 versus 1.348; P < 0.01) and protease improved FCR by 1.41% (1.324 versus 1.343; P < 0.05), but in combination, both feed enzymes improved FCR by 3.52% (1.317 versus 1.365; P < 0.005) relative to the negative control. It is noteworthy that in the first experiment, whole wheat inclusions did not significantly influence starch digestibility but phytase inclusions increased distal ileal starch digestibility by 5.10% (0.948 versus 0.902; P < 0.05) in pre-pellet and by 3.85% (0.943 versus 0.908; P < 0.05) in post-pellet whole grain treatments.