Volatile fatty acids and lactic acid in the rumen of dairy cows receiving a variety of diets

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Abstract
When hay alone was fed to dairy cows there was little variation in concentration of volatile fatty acids at hourly intervals after feeding[long dash]values ranging from 8.1 - 12.1 meq/100 ml rumen liquor with different diets. Diets containing small amounts of hay, or finely ground hay, produced a wide range of concentrations, from 5.6 -20.0 and 7.0 - 21.3 meq/100 ml,respectively. Only traces of lactic acid (< 1 mg/100 ml rumen liquor) were found with all diets except those containing large amounts of flaked corn (maize) when peak concentrations of 95 - 270 mg occurred 2 hours after feeding, and rapidly disappeared. The mixture of acids produced was characteristic of the fermentation in the rumen. Mean molar percentages of the acids varied on the different diets as follows: acetic, 40.6 - 73.7; propionic, 16.5 - 39.1; butyric, 6.6 - 13.9; higher acids, 2.5 - 12.7. Values for acetic and propionic acids varied inversely, and the ratio of acetic to propionic acid decreased with the decrease in ratio of fiber to starchy concentrates, except where finely ground hay was fed. In general, concentrations of butyric and higher acids increased with increased dietary protein.