SITE AND EXTENT OF CELL-WALL NEUTRAL MONOSACCHARIDE DIGESTION IN DAIRY-COWS RECEIVING DIETS WITH ROLLED CEREAL-GRAINS

The effect of source of rolled cereal grain on the site and extent of cell-wall neutral monosaccharide (CWM) digestion in dairy cows was inv estigated in this study. Three diets were formulated on a starch equiv alent basis to contain (percentage of diet dry matter, DM) rolled oats (36%), rye (29%) or barley (31.5%). The remainder of diet DM was made up of grass hay (35.5-39.5%) and coconut meal (26.5-29.5%). Diets con taining rolled oats, rye and barley were designated 0, R and B, respec tively. Three dairy cows (two lactating, one non-lactating) equipped w ith ruminal, duodenal and ileal cannulae were used in a 3 x 3 Latin sq uare design to measure the digestibilty of organic matter (OM) and CWM in the whole tract and its partition in the rumen, and in the large i ntestine. Titanium (IV)-oxide and chromium ethylenediamine tetra-aceti c acid were used as flow markers. In all diets, CW glucose was more di gestible in the whole tract and in the rumen than CW xylose. Apparent whole-tract digestibilities of OM (0, 69.8%; R, 73.8%; B, 73.0%) and t otal CWM (0, 72.7%; R, 79.5%; B, 77.7%) were lower (P<0.01) for 0 comp ared with R and B. Ruminal characteristics (pH values and NH3-N) were only slightly different among diets, indicating similar conditions for microbial CWM fermentation. However, apparent ruminal CWM digestibili ties were lower for 0 as compared with R and B. The greatest differenc es were obtained for xylose (0, 39.7%; R, 59.5%; B, 52.6%; P<0.05) and for glucose (0, 61.1%; R, 70.2%; B, 67.3%; P<0.05). In the small inte stine, both positive and negative digestibilities were observed. Altho ugh numerical values varied largely among and within CWM, no significa nt contribution of the small intestine to total CWM digestion could be detected. The contribution of the large intestine to total CWM digest ion was similar across diets, 20.6%, 23.2% and 18.2% for 0, R and B, r espectively. It was concluded that CWM from oats per se were less dige stible than CWM from rye and barley in all parts of the gastrointestin al tract and that xylose was the least digestible CWM.