NUTRIENT FLUXES IN SPLANCHNIC TISSUE OF DAIRY-COWS - INFLUENCE OF GRASS QUALITY

A crossover design was used to investigate tl-Le effects of high (450 kg of N/ha) or low (150 Bg of N/ha) N fertilization of ryegrass on fer mentation and nutrient fluxes in splanchnic tissue of dairy cows fed t hose grasses. Grass that was fertilized with the high amount of N cont ained more N and less sugar than did grass that was fertilized with le ss N. In lumen fluid, the concentration of NH3 N was lower for ryegras s that was fertilized with the low amount of N, The NH3 release by por tal-drained viscera and urea synthesis in the liver were higher for Co ws fed ryegrass that was fertilized with the high amount of N. The con centration of NH3 N in rumen fluid, NH3 N release in portal-drained vi scera, urea synthesis in ene liver, urea release from the liver, and u rea concentrations in milk were highly correlated. The release of acet ate and propionate in portal-drained viscera was similar for both gras ses and was well correlated with the proportion of volatile fatty acid s in rumen fluid. The proportion of butyrate in rumen fluid was closel y correlated with the release of butyrate and beta-hydroxybutyrate in pori;al-drained viscera. Glucose synthesis in the liver indicated gluc oneogenesis from amino acids, which corresponded well with urea synthe sis in the liver. For the grass fertilized with more N, availability o f energy sources for rumen microbes was low, and, therefore, cows did not use the N in that grass efficiently.