The interactions of exogenous phytase with whole grain feeding and effects of barley as the whole grain component in broiler diets based on wheat, sorghum and wheat-sorghum blends

Abstract

The objectives of this experiment were two-fold; the first was to evaluate exogenous phytase in either conventional or whole grain diets as a 2 × 2 factorial treatment array. Wheat-sorghum blended rations containing 12.5% ground or whole barley were offered without and with 1000 FTU/kg exogenous phytase. The second objective was to evaluate barley as the whole grain component in diets based on wheat, sorghum and equal wheat-sorghum blends as a 3 × 2 factorial treatment array. Rations based on wheat, sorghum and wheat-sorghum blends were offered as an intact pellet containing 12.5% ground barley or offered as a mix of 12.5% whole barley and a pelleted concentrate. Each of the dietary treatments was offered to 7 replicates (6 birds per cage) of male Ross 308 chicks from 7 to 28 days post-hatch. Treatment effects on growth performance, gizzard and pancreas weights, gizzard pH, bone mineralisation, nutrient utilisation, digestibility coefficients of starch and protein (N) and starch:protein disappearance rate ratios in four small intestinal segments (proximal and distal jejunum, proximal and distal ileum), excreta dry matter and incidence of dilated proventriculi were determined. In the 2 × 2 analysis there was a significant (P < 0.025) treatment interaction for FCR. Phytase addition to whole barley diets improved FCR by 3.20% (1.362 versus 1.407) but phytase compromised FCR by 3.11% (1.391 versus 1.349) in ground barley diets. Similarly, treatment interactions (P < 0.002 − < 0.001) were also observed for energy utilisation (AME, ME:GE ratios, AMEn) where phytase generated positive responses in the context of whole grain feeding but not in conventional diets. In the 3 × 2 analysis, whole barley significantly increased relative gizzard weights by 22.5% (16.96 versus 20.77 g/kg; P < 0.001) and significantly reduced (P < 0.05) the incidence of dilated proventriculi from 4.76% to zero. However, whole barley compromised growth performance. There were significant treatment interactions (P < 0.001) for parameters of energy utilisation as whole barley significantly enhanced energy utilisation (AME, ME:GE ratios, AMEn) in birds offered sorghum-based diets but this was not the case with wheat or blended diets. Wheat-based diets generally supported better protein and starch digestibility coefficients with significant advantages being observed in some small intestinal segments in comparison to sorghum and blended diets. For example, wheat-based diets generated significantly higher protein digestibility in the ileum (P < 0.001) than birds offered sorghum or blended diets. Likewise, wheat-based diets generated significantly higher starch digestibilities in the proximal jejunum and distal ileum (P < 0.001) than birds offered sorghum or blended diets. Whole barley reduced water intakes by 9.72% (325 versus 360 g/bird/day; P < 0.01) and significantly increased excreta dry matter in wheat-based diets from 22.1 to 25.1% (P < 0.001) but there was a decrease from 26.08 to 24.50% (P < 0.05) in sorghum-based diets. Therefore, it may be concluded that phytase is more effective in whole grain diets than conventional diets. Whole barley increased gizzard weights, reduced the incidence of dilated proventriculi and significantly improved energy utilisation in sorghum based diets.