Sucrose supplements in cattle given grass silage-based diet. 2. Digestion of cell wall carbohydrates

Abstract

The effect of sucrose supplements on cell wall digestion was studied in a 4 × 4 Latin square experiment using male cattle fitted with a rumen cannula and a simple T-piece duodenal cannula. The control diet (C), fed at the level of 5.3 kg dry matter (DM) day −1, consisted of grass silage (700 g kg −1 DM), barley (240 g kg −1 DM) and rapeseed meal (60 kg −1 DM). The three other diets were supplemented with 1.0 kg of sucrose given twice daily (S), or twice daily with 0.25 kg day −1 of sodium bicarbonate (B), or as a continuous intraruminal infusion (I). Duodenal flows of neutral detergent fibre (NDF), acid detergent fibre (ADF), cellulose and hemicellulose were estimated using chromium (Cr)-mordanted straw and CoEDTA as flow markers. The degradation characteristics of silage DM, NDF and ADF were determined by incubating the samples in nylon bags in the rumen for different periods of time. Sucrose supplements increased duodenal flows of NDF ( P < 0.1), ADF ( P < 0.05), cellulose ( P < 0.05) and hemicellulose ( P < 0.1) compared with Diet C. In spite of partial compensation for the reduced rumen digestion in the hindgut, the total digestibility of cell wall carbohydrates decreased when sucrose was included in the diet. Among the sucrose diets, bicarbonate supplement alleviated the adverse effect of sucrose on fibre digestion and the values observed with Diet B were similar to those with Diet C. Continuous infusion of sucrose had a similar adverse effect on fibre digestion to Diet S. Feeding Diets S and I decreased the disappearance of silage DM, NDF and ADF from nylon bags, especially after incubation periods of 12–48 h, and as a result the rate constants for the degradation of different silage components were lower ( P < 0.05) than with Diets C and B. Sucrose supplements increased the lag time of fibre digestion.