Changes in fermentation pathways from acetate toward propionate production and in microbiota from fibrolytic toward amylolytic species were closely associated with ruminal dissolved hydrogen in lactating dairy cows. An unresolved paradox was that greater dissolved hydrogen was associated with greater numbers of methanogens but with lower gaseous methane emissions.

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Active plant metabolites (APM) are recognized as modifiers of ruminal microbial fermentation including methanogenesis and biohydrogenation of fatty acids (FA). Coleus amboinicus Lour. leaves (CAL) are rich in several APM, which could serve as ruminal fermentation modulators. A phytochemical analysis showed that CAL contain phenolic acids (10.4 mg·g-1 dry matter [DM]; high in rosmarinic acid), flavonoids (2.6 mg·g-1 DM), diterpenes (2 mg·g-1 DM), and linolenic acid (35.4 g (100 g)-1 FA). This study aimed to investigate the effect of CAL on ruminal methanogenesis and biohydrogenation as well as basic fermentation characteristics and microbial populations. The in vitro experiment was carried out using Hohenheim gas test system with 40 mL of buffered ruminal fluid incubated for 24 h at 39 °C in anaerobic conditions. Approximately 400 mg (DM basis) of total mixed ration (TMR) was used as a control substrate and the CAL substrate was used at doses of 10, 20, 40, and 80 mg DM replacing equal amounts of TMR. Addition of CAL decreased methane production up to 30% linearly as the amount of CAL increased (P < 0.05). In vitro dry matter digestibility and ammonia tended to increase with increasing doses of CAL. Concentration of total volatile fatty acids was not affected by the CAL although there appeared to be a minor positive linear trend; however, acetate, butyrate, and isobutyrate proportion increased quadratically (P < 0.001). CAL tended to linearly increase α-linolenic acid and conjugated linoleic acid as well as increased stearic acid concentration in buffered ruminal fluid. CAL particularly increased total protozoa and bacterial populations during fermentation, but inhibited methanogens. It is concluded that the CAL may be promising to be used as a feed additive to decrease methanogenesis as well as biohydrogenation of FA in the rumen.

No abstract

The efficacy of methane (CH 4 ) suppression using medium-chain fatty acids (MCFA) remains inconclusive, despite a number of studies on this topic are available. We thus carried out a meta-analysis to integrate the published data on different concentrations and types of MCFA such as lauric acid and myristic acid, which investigated ruminal methanogenesis and fermentation in in vitro and in vivo experiments. In vitro MCFA sources were classified either as pure MCFA (lauric acid, myristic acid and their combinations) or as natural MCFA-rich oils (canola oil enriched with lauric acids, coconut oil, krabok oil and palm kernel oil). The MCFA sources used in the in vivo studies were coconut oil, lauric acid, myristic acid and the combination of lauric and myristic acids. A total of 41 studies (20 in vitro and 21 in vivo studies) were compiled in our database, which included the data on CH 4 emission, digestibility, ruminal fermentation products and microbial populations. The results showed that the amount of CH 4 production per unit of digested organic matter decreased linearly under in vitro conditions (p < .01) and tended to decrease quadratically under in vivo conditions (p < .07) with increasing doses of MCFA. Populations of protozoa (p < .01) in both in vitro and in vivo responded negatively in a linear manner, whereas Archaea population diminished quadratically (p = .04) only in the in vitro conditions with increasing doses of MCFA. Increasing dietary MCFA concentrations also reduced the fibre digestibility linearly (p < .05) in both in vitro and in vivo conditions. CH 4 production for different sources of MCFA decreased in following order: coconut oil > lauric acid > myristic acid > mixed lauric and myristic acids > palm kernel oil > canola oil enriched with lauric acids > krabok oil. It can be concluded that the effect of MCFA on ruminal methanogenesis depends on the amount and type of MCFA.