Estimasi Emisi Gas Metan yang Dihasilkan dari Fermentasi Hijauan Tropis dalam Rumen In Vitro Melalui Komposisi Asam Lemak Terbang
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Rumen is the home to billions of microbes, including bacteria, methanogens, protozoa and fungi. These microbes breakdown feed to produce volatile fatty acids (VFA), carbon dioxide, ammonia and methane (CH4). Metabolic hydrogen in the form of reduced protons (H) is used during CH4 formation as well as during VFA synthesis. Therefore, VFA molar proportion in the rumen is stoichiometrically related to CH4 emission. The aim of this study was to evaluate methane emission between experimental and model estimates. The data sets were obtained from a published literature. Samples used were leaves from 27 tropical plant species. Model comparison was based on Duncan’s test. Prediction error was conducted by computing mean square prediction error (MSPE) and root mean square prediction error (RMSPE). Results showed that linear equation of Moss model to CH4 observed before adjustment was y = 0.4231x – 3.1762 with R2 = 0.4645, whereas Hegarty model to CH4 observed before adjusment was y = 0.3735x – 3.2963 with R2 = 0.4778. Further, linear equation of Moss model to CH4 observed after adjusment was y = 0.8446x – 4.6719 with R2 = 0.6619, while Hegarty model to CH4 observed after adjustment was y = 0.7405x – 4.8011 with R2 = 0.6714. Validation assessment 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%. This study demonstrated that the low or high methane emission can be estimated by VFA composition with a sufficient accuracy. Adjusment by considering H2 recovery lowered the bias significantly. Comparison of predicted versus observed CH4 production showed that Moss model had closer to the ideal line (where predicted values are the same with the observed values) than Hegarty model.