The effect of dietary wheat middlings and enzyme supplementation - II: Apparent nutrient digestibility, digestive tract size, gut viscosity, and gut morphology in two strains of leghorn hens

An experiment was conducted with two strains of Leghorn hens, DeKalb Delta (D) and Hisex White (H), to investigate the effect of a commercial poultry enzyme preparation (EZ; xylanase plus protease) on the digestibility of pro tein, fat, Ca, and P and to determine any changes in the relative size of t he digestive tract, gut morphology, and gut viscosity (GV) of birds fed whe at middlings (WM) over an 18-wk period. Three hundred birds (150 birds per strain) were randomly assigned to six diets: Diet 1, control (corn-soybean) ; Diets 2 and 3, 8% and 16% WM, respectively; Diet 4, 8% WM and 0.1% enzyme (EZ); and Diets 5 and 6, 16% WM and 0.1% and 0.2% EZ, respectively. There were five replicates per diet per strain. At 50 wk, protein digestibility i ncreased significantly with supplementation of EZ, but, at 60 wk, all respo nses were similar. Protein digestibility was greater in DeKalb Deltas for W M with EZ compared with Hisex on the same treatment. Fat digestibility was greater for Diet 1 than the other diets at 50 wk but showed a similar respo nse at 60 wk. The PI strain showed a reduction in fat digestibility with WM diets with EZ. The control diet showed greater Ca digestibility than the o ther diets at 50 wk but did not differ at 60 wk. Phosphorus digestibility i ncreased significantly for WM diets with or without EZ at 60 wk. Intestinal weight was significantly higher for WM with or without EZ at 50 wk, but wa s equal to the control diet at 60 wk. At 60 wk, gizzard weights (GW) were a lso lower in birds fed WM and WM with EZ compared with birds fed the contro l, but GV was not affected by dietary treatments. Histological observations on jejunum of birds fed WM without EZ showed shortening, thickening, and a trophy of the villi, all of which improved when EZ was included in the diet . Availability of some nutrients in WM diets was improved with supplementat ion of enzyme. Gastrointestinal (GI) tract and organ size were increased, a nd gut morphology appeared to be improved.