Optimisation of the Gc Method for Assessing Volatile Fatty Acids in Rumen Liquid

Accurate determination of the volatile fatty acids (VFA) content of the rumen liquid is indispensable for assessing feedstuffs utilization and effects at ruminal level. Moreover, nowadays feeding strategies require more detailed information such as post-prandial dynamics of VFAs, content of minor VFAs, etc. which leads to the need for precise, rapid and economic determination. In this context, the purpose of this study was to optimize the current GC method by modifying chromatographic conditions and sample preparation in order to reduce the analysis time and the reagents amounts.The optimized method was practically applied by testing VFA from rumen liquid of fistulated wethers challenged with sudden change of the concentrates: forage ratio of the diet from 20:80 to 50:50 (diet 1), 100:0 (diet 2) and 0:100 (diet 3). Rumen content was sampled 4 hours after the morning feeding, prepared and analyzed using the optimized method. Acetic acid content was reduced by diet 1 (72.51 % to 67.46 %) and diet 2 (68.11 % to 64.15 %) whereas diet 3 induced an increase (from 69.95 % to 72.16 %), results that are consistent with the known effects of concentrates: forages ratio. Propionic acid tended to express inverse effects, also consistent with the previous literature reports. These preliminary results showed that the modified GC method enables rapid and sensitive VFA determinations.