Determination of the Volatile Fatty Acid Content in the Rumen Liquid: Comparison of Gas Chromatography and Capillary Isotachophoresis

Abstract

Two analytical procedures for determining volatile fatty acids in the rumen liquid were compared: capillary isotachophoresis (ITP) and gas chromatography. Acetic acid, propionic acid, butyric and valeric acids were determined. No significant differences (n = 53, P ≥ 0.05) have been identified in the amounts of acetic and propionic acids and the results are highly consistent. For butyric acid, the method of gas chromatography yielded higher results with a constant error of approximately 0.5 mmol/l in the whole range of concentration. In terms of diagnostics, however, this size of error is non-significant. In the case of valeric acid a proportional error was found. Gas chromatography yielded higher values, the difference being greater for the low values while for the higher values the results are almost identical. However, valeric acid is a minor acid and its determination is of secondary significance to rumen fermentation assessment. The gas chromatography method is able to clearly differentiate between n and iso forms in the case of butyric and valeric acids. It can be stated that the two analytical methods yield comparable results and both can be used for the needs of practical diagnostics.