Measurement of Certain Metabolic Organic Acids in Forage, Silage, and Ruminal Fluid by Gas-Liquid Chromatography

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Abstract
Gas-liquid chromatography was found applicable for quantifying lactic, oxalic, malonic, fumaric, succinic, malic, alpha-ketoglutaric, and citric acids in forage, silage and ruminal fluid. Aqueous extracts of ground and dried forage, extracted at 55 C, were lyophilized and the organic acids contained in the residue were esterified with methanol and hydrochloric acid. The esters of the acids were then chromato-graphed according to a previously described method. Aqueous extracts of silage and protein-free filtrates of ruminal fluid, prepared by acetone-ethanol precipitation, were prepared and analyzed similarly. Recoveries of all acids, determined by spiking samples with known amounts of organic acids, were near 100%. Two groups of forage samples, containing both freeze- and oven-dried samples, contained similar amounts of organic acids and the differences due to method of drying were analogous for both groups. Lactic acid measured in silage samples was comparable to that measured in the same samples by the FeCl3 and p-hydroxydiphenyl methods. Interfering peaks were encountered when some ruminal fluid samples were chromatographed.