Fate of Carbon Passing Through the Glucose Pool of Rumen Digesta

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Abstract
The metabolism of the free glucose pool in rumen digesta from sheep fed roughage rations was studied by adding an insignificant quantity of glucose as uniformly labeled 14C-glucose of high specific activity to in vitro incubation systems. In all experiments wherein only trace quantities of glucose were added to digesta, most of the 14C-glucose entered acetate. This was true whether label was presented either as a single dose or by continuous addition over a period of 2 hr. Digesta collected at all times after feeding either once daily or at hourly intervals gave similar glucose dissimilation patterns. If, however, a relatively large quantity of carrier glucose was added together with the tracer, the 14C-acetate: 14C-propionate ratio was reduced by a factor of about 10. Physical removal of most of the protozoa from digesta generally had little effect on the dissimilation of 14C-glucose added in tracer amounts, but in one experiment there was a decreased turnover of the free glucose pool and a marked reduction in 14C entering butyrate. The paucity of 14C entering propionate when only trace amounts of glucose were added to digesta suggests that this acid was largely formed from substrates whose carbon did not equilibrate with that in free glucose or with that in intermediates of free glucose metabolism.

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