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

Abstract

In a 4 × 4 Latin square experiment, four Friesian male cattle fitted with rumen and duodenal cannulas were given a basal diet of grass silage, barley and rapeseed meal (700, 240 and 60 g kg −1 total dry matter (DM)) at the rate of 5.3 kg DM day −1 (Diet C) or supplemented with 1.0 kg day −1 of sucrose given either twice daily (Diet S), twice daily with 0.25 kg day −1 of sodium bicarbonate (Diet B) or as a continuous intraruminal infusion (Diet I). Duodenal flow was estimated using chromium (Cr)-mordanted straw and cobalt ethylenediamine tetracetic acid as digesta flow markers, and purine bases of nucleic acids as microbial markers. Samples of rumen fluid were taken for estimation of rumen pH and the concentrations of ammonia nitrogen (N), volatile fatty acids and lactic acid. 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 averaged 0.68 and was not significantly affected by the diet. Sucrose supplements decreased rumen pH ( P < 0.05), ammonia N 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, the concentration of lactic acid and molar proportion of butyrate were highest with Diet S. Sucrose supplements increased the rumen liquid dilution rate ( P < 0.01) and liquid outflow ( P < 0.001) from the rumen. Feeding sucrose diets 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. The efficiency of microbial N synthesis (g N kg −1 OM apparently digested in the rumen) was non-significantly increased by sugar supplements. Among the sucrose diets, continuous infusion of sucrose tended to decrease ammonia N concentration and stimulate microbial N synthesis more than feeding sucrose twice daily.