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Journal of Experimental Biology 19,186-198 (1942)
Published by Company of Biologists 1942

The Fluctuation of pH and Organic Acids in the Rumen of the Sheep

A. T. PHILLIPSON ¹

¹ Institute of Animal Pathology and the Unit of Animal Physiology, Cambridge

1. The pH of the ingesta of the rumen varies in a regular manner; the speed and extent of the variation depends upon the diet.

2. The changes of pH reflect the fluctuations in the quantities of organic acids that accumulate in the ingesta as a result of fermentation of food in the rumen.

3. Lactic acid accumulates temporarily in the rumen when mangolds and cabbage are included in the ration. The production of lactic acid is accompanied by an abrupt and marked fall of pH.

4. Volatile acids are constantly present in the rumen ingesta; they increase in quantity after feeding and decrease with fasting.

5. The rate of fermentation in the rumen depends upon the diet; it is most rapid when mangolds and cabbage are fed in addition to roughage, less rapid when bran and oats form the concentrated part of the ration, and least rapid when hay alone is fed.

6. The ingesta of the rumen are more acid when sheep are grazing on young pasture grass than when they are stall fed.

7. The osmotic pressure of the ingesta of the rumen varies inversely with the pH.