Sucrose supplements in cattle given grass silage-based diet. 3. Rumen pool size and digestion kinetics

Abstract

The effects of sucrose supplements on rumen pool sizes and digestion kinetics were studied in a 4 × 4 Latin square experiment in male cattle fitted with rumen and duodenal cannulas. The basal diet (Diet C), fed at the level of 5.3 kg dry matter (DM) day −1, was comprised of grass silage, barley and rapeseed meal (700, 240 and 60 g kg −1 DM, respectively). The other three diets were supplemented with 1.0 kg day −1 of sucrose administered twice daily (Diet S), or twice daily with 0.25 kg day −1 of sodium bicarbonate (Diet B), or as a continuous intraruminal infusion (Diet I). Pool sizes of rumen digesta and its components, and the digestion kinetics of cell wall carbohydrates, were derived from rumen evacuation. The potential digestibility of rumen digesta and faeces was determined by incubating the samples for 240 h in nylon bags in the rumen. The main effect of sucrose supplements was to increase the rumen pool size of DM and fibre constituents. The greater rumen pool size of neutral detergent fibre (NDF) and acid detergent fibre (ADF) with sucrose diets consisted mainly of digestible NDF and ADF. Inclusion of sodium bicarbonate in the diet almost completely alleviated the effect of sucrose on rumen pool sizes. There were close negative correlations ( r 2 0.96–0.999) between the rumen pool size of cell wall components and in vivo digestibility of the corresponding component. The rates of digestion ( k d) were decreased by sucrose supplements. The values for k d of NDF were 0.0594, 0.0444, 0.0557 and 0.0448 for Diets C, S, B and I, respectively. The rate of passage ( k p) or its reciprocal, rumen residence time (RRT), were not significantly affected by the diet. Longer RRT was measured for digestible NDF (71.5 h) than for total NDF (61.7 h) and for indigestible NDF (49.7 h). The potential digestibility of DM, NDF and ADF of rumen ingesta and faeces was higher with Diets S and I than with Diets C and B. Faecal output of digestible NDF was greater with Diets S and I than with Diets C and B.