Distribution of Volatile Fatty Acids in Rumen Ingesta of Steers Fed Concentrate and Roughage Diets

Four steers were fitted with permanent ruminal cannulae and fed either an all-roughage or an all-concentrate diet. The ruminal concentration of volatile fatty acids and pH were compared from five intraruminal sites. The first sample was collected with a stomach tube, and samples from the four remaining sites were collected through the rumen cannula. Samples were collected 4 hr. and 8 hr. after the morning feeding. In most cases, the pH was highest in the stomach tube sample and was lowest near the surface of the rumen fluid in steers fed the roughage diet and lowest near the ventral floor of the rumen in those fed the concentrate diet. The concentration of volatile fatty acids in the hay-fed steers was highest near the top of the rumen fluid at the 8-hr, time, but no significant differences were observed at the 4-hr, sampling time. The concentration of volatile fatty acids in the grain fed steers was highest in the ventral portion of the rumen at both time periods. Comparison of the individual acids suggested differential fermentation rates for the two diets. Significant differences in volatile fatty acid concentrations among the sampling sites were observed but no general trend was apparent.