Effect of rate and extent of starch digestion on performance, physiology and behaviour of broilers and laying hens

The effect of rate and extent of starch digestion on broiler and laying hen performance, digestive tract physiology and feeding behaviour, with particular focus on the ileal brake activation, was assessed. Semi-purified wheat (WS, rapidly digested) and pea (PS, slowly digested) starch were combined to create six WS:PS ratios (100:0, 80:20, 60:40, 40:60, 20:80, 0:100) in treatment diets, and were fed to Ross 308 broilers for 28 days and Lohmann LSL-lite laying hens for 20 weeks. Mortality-corrected gain:feed ratio of broilers was maximized at 25% PS. Breast meat yield relative to live body weight increased linearly with dietary PS inclusion, while fat pad, and breast and thigh skin decreased in a linear fashion. Overall hen-day egg production increased linearly with PS, but it was maximized at 70% PS during the second half of the experiment. Feed:egg mass ratio was minimized at 26% PS (quadratic). Ileal brake activation potential was found in both broilers and laying hens. Increasing PS inclusion in broiler diets resulted in lower in-vivo starch digestibility, and quadratic responses in both crop pH (minimum at 55% PS) and ileum SCFA (maximum at 58% PS). Likewise, crop and ileum pH in laying hens increased with PS inclusion. Actual indications of ileal brake activation were not as clear. While most digestive tract morphological parameters increased linearly with PS in broilers, GLP-1 and PYY serum concentrations and small intestine transcript abundance were not affected by PS inclusion. Feeding behaviour of broilers was not affected either. Digestive tract parameters of laying hens responded with a combination of linear increasing and quadratic effects with maximum values in the mid-range of PS concentrations. In addition, serum GLP-1 also increased linearly, while PYY was maximized at 34% PS. However, dietary PS concentration did not affect feed passage rate. Likewise, laying hen day-time feeding behaviour was not affected by PS concentration, but night feeding behaviour increased with PS inclusion. In conclusion, the positive effect of including PS in poultry diets was confirmed, but L-cell activation and its consequences seem to differ between bird types and act in a different manner compared to mammal