Rumen Chemical and Microbial Characteristics of Steers Fed a Purified and a Natural Diet

Weekly ruminal samples were obtained from four steers during adaptation and maintenance, while fed equal amounts of a purified diet which contained urea as the sole source of dietary nitrogen or a natural diet of hay and concentrates. Ruminal samples were taken by stomach tube 4 hr. after eating. Total viable bacterial concentration, total protozoal concentration and numbers of certain species, volatile fatty acids, ammonia and pH were determined on each sample. Ruminal fill determinations were made with four cannulated steers fed the same diets. Bacterial concentration, molar percent of butyric plus higher VFA, total concentration of VFA and ammonia were increased significantly, while protozoa concentration, molar percent of acetic acid and pH decreased significantly when the steers consumed the purified diet. During several sampling periods protozoa could not be detected, and rumen fill tended to be greatest when steers were fed the purified diet. A significant cubic response for bacteria and protozoa concentrations was found during weeks on the diets, while a significant linear response was found for molar percent of propionic and butyric plus higher acids, total concentration of VFA and pH during this time.