Influence of ration form and nitrogen availability on ruminal fermentation patterns and plasma of growing bull calves

Nine rations containing three forms (ground hay, .2 to 2 cm; chopped hay, 6 to 10 cm; or all concentrate) and three percents (30, 45, and 60%) of rumen degradable nitrogen were fed to 54 Holstein calves (3 X 3 factorial) between 8 and 20 wk of age. Rumen fluid samples were obtained at 8, 11, 14, 17, and 20 wk of age and plasma at 14 and 20 wk of age. Rumen fluid acetate concentration was greatest for ground hay and lowest for concentrate; propionate was greatest for concentrate and lowest for calves fed ground hay. Calves fed concentrate had highest valerate and total volatile fatty acid concentration, whereas lactate concentration and pH were least for concentrate. Ruminal ammonia nitrogen increased with increasing ruminally degradable protein feedstuffs in the ration. Plasma acetate was highest for chopped hay and lowest for concentrate, whereas calves fed concentrate and ground hay were comparable with higher propionate and glucose concentrations than calves fed chopped hay. Plasma urea nitrogen was highest for calves fed 60% ruminally degradable protein.