Digestibility and energy value of cereal-based diets in relation to digesta viscosity and retention time in turkeys and chickens at different ages estimated with different markers.

Digesta viscosity, ileal transit time of digesta, apparent ileal protein digestibility and apparent metabolisable energy (AME(N)) of diets based on wheat and dehulled barley (WB), oats (O) or a mixture of these (WBO) fed as such or with enzyme supplementation in three- and six-week old turkeys and broilers were investigated. In addition, differences between ileal digestibility and AME(N) calculated by using titanium dioxide (TiO2), chromic oxide (Cr2O3) or acid insoluble ash (AIA) as indigestible markers were compared. Digesta viscosities were generally moderate reaching from 2.5 mPa x s to 7.3 mPa x s. The highest viscosities were observed in WBO diets. Viscosities were reduced with age in broilers, and were generally higher in turkeys than in broilers, especially at six weeks of age. Digesta retention time in ileum was elongated with age of the birds, pronouncedly in broilers. Oat inclusion to the diets decreased retention time especially in broilers at six weeks of age. Apparent ileal digestibility of protein ranged from 0.64-0.83, was lower at six weeks of age than at three weeks of age and generally lowest in O diets, especially in turkeys. AME(N) of the diets ranged from 11.2-13.4 MJ/kg being higher at six weeks of age than at three weeks of age. AME(N) of Diets O was the lowest but AME(N) of WBO diets was higher than that of WB diets indicating a synergistic interaction of cereals, this trend being more pronounced in broilers. Enzyme supplementation decreased viscosity and improved AME(N) in most diets, but did not affect ileal protein digestibility. Differences between ileal digestibility estimates obtained with TiO2 or Cr2O3 were small and mainly not significantly different from 0. AME(N) estimates were generally higher when calculated with Cr2O3 than with TiO2. AIA gave remarkably lower AME(N) values than TiO2 (the significant differences ranging from 0.24-0.94 MJ/kg). In addition, effects of markers on AME(N) estimates interacted with age of the birds and dietary treatments.