Assessment of methane estimation from volatile fatty acid stoichiometry in the rumen in vitro

Abstract

Rumen microbes breakdown feed to produce volatile fatty acids (VFA), carbon dioxide, ammonia and methane (CH4). Metabolic hydrogen in the form of reduced protons is used during CH4 formation as well as during VFA synthesis. Therefore, VFA concentration in the rumen may stoichiometrically be related to CH4 emission. The aim of this study was to evaluate methane emission between experimental and model estimates. Two stoichiometrical models for predicting CH4 from VFA were assessed, i.e. Moss et al. (2000) and Hegarty and Nolan (2007) models. The data sets were obtained from a published literature. Samples used were leaves from 27 tropical plant species. Prediction error was conducted by computing root mean square prediction error (RMSPE). Results showed that estimation model of Moss et al. (2000) had lower RMSPE value, i.e. 8.01%, than that of Hegarty and Nolan (2007) model, i.e. 10.73%. Variation of methane emission, i.e. the low or high methane can be estimated by VFA composition with a sufficient accuracy. Adjusment by considering H2 recovery lowered the bias significantly. It can be concluded that Moss model had better accuracy in predicting CH4 emission from VFA composition than that of Hegarty and Nolan model.