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 × 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. Fluid microorganisms were those that passed through eight layers of cheesecloth. Particle-associated microorganisms were obtained by chilling (0°C) squeezed particles before blending followed by four successive extractions with saline solution. Particle-associated microorganisms had a higher (P < .01) concentration of OM than fluid-phase microorganisms at both times. Bacterial fractions had a higher (P < .01) concentration of CP than the protozoal fractions. However, the total quantity of OM (mg/ml strained ruminal fluid equivalent; SRFE) was 2.4 to 12 times greater (P < .01) in the protozoal fractions than in respective bacterial fractions. The total quantity of CP (mg/ml SRFE) was 2.1 to 10.5 times greater in the protozoal fraction than in the bacterial fraction, and DAPA ranged from 1.3 to 4.9 times greater for the protozoal fraction. 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.
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Olubobokun et al. (1988) studied this question.