Continuous changes in straw carbohydrate digestion and composition along the gastrointestinal tract of ruminants

The digestion of carbohydrates in straw and their substituent acetic and phenolic acids was studied using a slaughter technique. Two goats received non‐alkali‐treated and alkali‐treated straws. The latter treatment increased the total apparent digestibility of cellulose by 56% and of hemicellulose by 110%. The ratio of cellulose to hemicellulose was altered in the rumen. For the non‐alkali‐treated straw the ratio decreased compared with the feed, whereas it increased for the alkali‐treated straw. The ratio was kept almost constant post‐rumen for both diets. The composition of the hemicellulose was also altered in the rumen compared with the straws fed. In particular the arabinose content decreased in both diets. Most of the polysaccharide digestion and absorption took place in the rumen. For the alkali‐treated straw a hindgut fermentation could also be noted, especially for cellulose. Klason lignin was lost in the rumen but was recovered in the small intestine. Ferulic acid was more readily lost in the rumen than p‐coumaric acid. Although acetyl groups were almost absent in the alkali‐treated straw, they could still be found in the digesta of the animal. The slaughter technique appears to be a useful method when working with partitioning of digesta in ruminant animals.