Characteristics of protozoal and bacterial fractions from microorganisms associated with ruminal fluid or particles

The effect of diet and time after feeding on the characteristics of protozoal and bacterial fractions associated with ruminal particle and fluid phases was determined using diaminopimelic acid (DAPA) as a bacterial marker. Four ruminally cannulated steers (three Brangus and one Hereford x Angus) weighing 400 kg were fed either an alfalfa hay diet or a higher-concentrate diet consisting of 40% corn, 20% soybean meal and 40% alfalfa. Whole ruminal contents were sampled 2 h and 23 h after initiation of feeding. Differential interference microscopy of resuspended microbial deposits indicated that the protozoal fraction contained bacteria associated with small feed particles, with protozoa and as clumps of bacteria. Results indicate that microorganisms associated with the protozoal fraction and particle-associated population make up most of the ruminal microbial mass.