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Rumen Digestion Studies

II. Studies in the Chemistry of Rumen Digestion¹

Departments of Dairy and Agricultural Chemistry, and the Institute of Nutrition, Michigan State College, East Lansing, Michigan

Studies of the chemical changes in the rumen suggest the following salient features regarding the fate of roughage in the ruminant digestive tract:

1. During the first 6 hours after feeding the predominant phenomenon was the rapid digestion of proteins and carbohydrates. Decomposition of cellulose began during this period but was not extensive.

2. The predominant phenomenon during the second 6 hours was the rapid disintegration of cellulose. Digestion of proteins and carbohydrates in this period paralleled the digestion of cellulose. Although small amounts of lignin may be attacked in the rumen, functionally the rumen is not a factor in lignin digestion.

3. Rumen digestion was observed to come to a standstill within 12 hours after feeding. Prolonging the digestion periods to 24 hours did not increase rumen digestion coefficients. Lignin apparently protects plant fragments from further action by rumen microflora.

4. Average rumen digestion coefficients for 8 trials at 12–14 hours after feeding were: dry matter 48.4, protein 59.6, nitrogen-free extract 65.2, crude fiber 27.2, cellulose 43.4, other carbohydrates 83.0 and lignin 3.1%.

5. After plant fragments pass from the rumen variable amounts of lignin may be digested, thereby exposing varying amounts of cellulose and protein to further digestion. Fecal digestion was observed to be quite variable even though rumen digestion of the same lots of hay was very constant.

6. The caecum plays only a supplementary role in the disintegration of roughage within the ruminant organism. An average of 11.6% of the cellulose and possibly 9.5% protein was observed to be digested in the caecum.

7. The production of fatty acids in the rumen was demonstrated. Maximum increases, after the increase due to digestion was eliminated, were 54.9% on an alfalfa hay ration and 281.7% on a beet pulp ration.

8. The rapid dissipation of fatty acids from the rumen together with the marked increases noted suggests that fatty acids may make a highly significant contribution to the nutrition of the ruminant either as an intermediate or end product of digestion.

² Present address, University of Chicago, Chicago, Illinois.

Manuscript received 17 July 1947.