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Ruminal Flora Studies in the Sheep

X. Influence of Nitrogen Intake upon Ruminal Function^{1, 2,}

Animal Husbandry Department, Agricultural Experiment Station, Utah State University, Logan, Utah

Columbia wethers, confined in individual pens, were fed a constant amount of a semipurified ration in which only the nitrogen content was varied. Three of the animals were fed additional casein per duodenum as the ingested nitrogen was reduced to maintain the total nitrogen input constant, and thereby minimize variation in the recycled nitrogen.

The dry matter intake and rate of eating of the sheep so supplemented per duodenum remained almost constant throughout the range of diets fed, in which the nitrogen varied stepwise from 12.2 to 2.5 gm/day. The dry matter intake and the rate of eating of the unsupplemented sheep, in contrast, were both greatly reduced when the nitrogen intake decreased below 6 gm per day.

On the basis of differences in data between the supplemented and unsupplemented sheep, it was estimated that at least 3.5 gm of nitrogen per day was recycled to the rumen.

A strong relationship was shown between nitrogen intake and the rate of digestion of cotton thread in the rumen. This rate followed changes in fermentative activity, as shown by pH changes. Neither the maximal nor minimal rate was attained, although these were approached.

The concentration of ruminal bacteria, as shown by direct counts, was positively and significantly (P < 0.001) correlated with the nitrogen intake, both before and 8 hours after feeding; more than a tenfold decrease occurred within the range of nitrogen intake fed.

The changes in bacterial concentration then correlated significantly with cotton thread cellulose digestion. It is concluded that within the system examined, where close control was attained over recycled nitrogen and total intake, and hence substrate concentrations, the direct count of ruminal microorganisms reflects the functional capacity of the rumen.

² The authors are grateful to the Dow Chemical Company, Midland, Michigan, whose generous financial support made the project possible.

³ Present address: Institute of Agriculture, University of Western Australia. Nedlands, Western Australia.

Manuscript received 6 November 1961.