Sucrose supplements in cattle given grass silage-based diet. 1. Digestion of organic matter and nitrogen

Abstract

In a 4 X 4 Latin square experiment, 4 male Friesian cattle with rumen and duodenal cannulae were given a basal diet of grass silage 700, barley 240 and rapeseed meal 60 g/kg total DM, at the rate of 5.3 kg DM/day (diet C) or supplemented with sucrose 1.0 kg/day given twice daily (diet S), twice daily with sodium bicarbonate 0.25 kg/day (diet B) or as a continuous intraruminal infusion (diet I). Duodenal flow was estimated using chromium mordanted straw and cobalt-EDTA as digesta flow markers, and purine bases of nucleic acids as microbial markers. Sucrose supplements increased the amount of organic matter (OM) entering the duodenum (P 0.05) and voided in faeces (P 0.001). The proportion of digestible OM apparently digested in the rumen was 0.68 and was not affected by diet. Sucrose supplements decreased rumen pH (P 0.05), ammonia nitrogen concentration (P 0.001) and molar proportions of acetate (P 0.001) and isovalerate (P 0.01), and increased those of butyrate (P 0.01) and valerate (P 0.05). Among the sucrose diets, concentration of lactic acid and molar proportion of butyrate were highest with diet S. Sucrose supplements increased rumen liquid dilution rate (P 0.01) and liquid outflow (P 0.001) from the rumen, and increased (P 0.05) the quantities of non-ammonia N and microbial N entering the small intestine, and the amount of N subsequently excreted in faeces. Efficiency of microbial N synthesis (g N/kg OM apparently digested in the rumen) was non-significantly increased by sucrose supplements. Among the sucrose diets, continuous infusion of sucrose decreased ammonia N concentration and stimulated microbial N synthesis more than feeding sucrose twice daily.