Effects of Addition Level and Chemical Type of Propionate Precursors in Dicarboxylic Acid Pathway on Fermentation Characteristics and Methane Production by Rumen Microbes in Vitro (Report‪)‬

INTRODUCTION Methane (C[H.sub.4]) is one of the most important greenhouse gases and domestic ruminants are responsible for 25% of these emissions (Makkar and Vercoe, 2007). Since its release to the atmosphere represents an energy loss of between 2% and 15% of ingested gross energy (Van Nevel and Demeyer, 1996) reducing its emission would benefit both ruminant production and environment (Van Nevel and Demeyer, 1996). Ionophores and unsaturated fatty acids (Demeyer and Fievez, 2000), anthraquinones (Kung et al., 2003), sulphur-containing amino acids (Takahashi, 2001), inhibitors of methanogenic archaea (Miller and Wolin, 2001) and inhibitors of oxidative pyruvate decarboxylation (Ungerfeld et al., 2003b) have been studied as potential feed additives to suppress C[H.sub.4] production in the rumen. Although some chemicals are capable of decreasing the ruminal C[H.sub.4] production, most of them not only depress microbial activities or population but also depress fiber digestibility (Chen and Wolin, 1979; Hinto, 1981).