Influence of the nature of forage and concentrate on the digestive interactions measured in sacco and in vivo

Reticulo-ruminal digestive interactions in complete mixed diets were studied in goats using various approaches. The nylon bag technique was used and the results were compared with stomach digestion estimated by duodenal flow from the same goats. Basal diets were composed of maize stover silage (MS) or alfalfa hay (AH) combined with 0, 30, or 60% of three types of concentrate, rich in rapidly (RS) or slowly (SS) degradable starch, or in digestible fibre (DF). Effective degradation (ED) of dry matter, structural carbohydrate (SC), neutral detergent soluble (NDS) and starch of roughage and concentrate were estimated. Significant decreases in ED of SC from roughage and concentrate were seen when the level of concentrate was increased in the basal diet. Compared with the duodenal flow technique, the in sacco measure overestimated the decrease in the SC degradation rate. Degradation of SC after 48 h of incubation in nylon bags was a better predictor than ED for SC duodenal digestibility. The in sacco method underestimated starch degradation of SS. Effective degradation of starch in SS has confirmed higher amilolytic activity after the (AH + SS) vs. (MS + SS) diets which had already been observed from in vivo duodenal digestion data.