Four sheep were fed 1,200 or 2,400 g air-dried alfalfa pellets/day in a crossover experimental design. After an intraluminal dose of 51Cr-EDTA, 103Ru-phenanthroline (103Ru-P), and 35S-sulphate, sequential samples of rumen fluid, digesta and microbes were taken for determination of pool sizes and dilution rates of the markers of these fractions. In addition, fecal samples were taken from 48 to 100 h after dosing. Level of intake did not significantly affect apparent digestibilities of dry matter or N, but the dilution rate of the fluid phase marker, 5lCr-EDTA, was increased by 54%, and the retention time of the particulate phase marker 103Ru-P, was decreased by 25% at the higher intake. Retention times of 103Ru-P in rumen digesta were highly correlated with those of 103Ru-P in feces. Lignin retention time in rumen digesta was also reduced by 18% at the higher feeding level. Significant reductions in the retention time of rumen microbial 35S, and rumen digesta 35S were observed at the higher feed intake. However, the pattern of decline with time of In 35S activity was curvilinear rather than linear. Interrelationships among the various markers are discussed.
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Mudgal et al. (1982) studied this question.