The effects of intraruminal infusions of sucrose and xylose on nitrogen and fibre digestion in the rumen and intestines of cattle receiving diets of grass silage and barley

Authors

• Pekka Huhtanen Department of Animal Husbandry, University of Helsinki, SF-00710 Helsinki, Finland

DOI: https://doi.org/10.23986/afsci.72274

Abstract

Two male cattle (live weight 240 kg) fitted with rumen and simple T-piece duodenal cannulas were given a basal diet of 12 kg of silage (227 g/kg DM, 25.7 g N/kg DM), 1 kg of rolled barley and 100 g of mineral mixture. In addition to the basal diet, 0, 450 or 900 g/d of either sucrose or xylose was continuously infused intraruminally. The amount of organic matter (OM) entering the duodenum (P < 0.001) and excreted in the faeces (P < 0.01) was linearly increased with the increased sugar infusion. The proportion of digestible OM apparently digested in the rumen averaged 0.694, and did not differ (P > 0.05) with the level or type of sugar. Rumen ammonia concentration and molar proportions of isovalerate were decreased (P < 0.001) with increased sugar level. The decrease in the ammonia concentration was slightly less (P < 0.05) with xylose than with sucrose. Molar proportions of acetate, propionate and butyrate were not affected by the sugar level but sucrose produced a lower (P < 0.05) proportion of acetate and higher (P < 0.01) proportion of butyrate than did xylose. There was a net loss of N (11.6g/d) between the mouth and duodenum when the basal diet was consumed alone but a net gain (21.6 g/d) with the high level of sugar infusion. Microbial N flow at the duodenum, measured on the basis of RNA purine bases, increased linearly (P <0.001) with sugar level. The efficiency of microbial N synthesis (g N/kg OM apparently digested in the rumen) was 24.0, 29.1 and 30.0 (P > 0.05) for sugar levels of 0, 450 and 900 g/d, respectively. The amount of microbial N produced was closely related to rumen ammonia concentration (r—0.86; P < 0.001) and outflow of water at the duodenum (r 0.83; P <0.001). The amounts of neutral detergent fibre (NDF) and acid detergent fibre (ADF) flowing at the duodenum (P < 0.01; P < 0.001) and excreted in the faeces (P < 0.05) were increased linearly with sugar level. The increased amounts of fibre digested in the large intestine with sugar infusions were insufficient to compensate for the reduced digestion in the rumen and, as a result, overall digestibilities of NDF and ADF were lower (P < 0.05). The effect of sugar level on the disappearance of silage N-free OM was consistent with the in vivo digestibility of fibre, although the extent of reduction seemed to be less in nylon bag incubations.