Rumen microbial responses in fermentation characteristics and production of CLA and methane to linoleic acid in associated with malate or fumarate

An in vitro incubation in batch was conducted to investigate the effect of propionate precursor (malate or fumarate) on fermentation characteristics, and production of CLA and methane by rumen microbes when incubated with linoleic acid (C18:2). Sixty milligrams of CC18:2 alone (LA), 60mg C18:2 with 24mM malic acid (M-LA), or 60mg C18:2 with 24mM fumaric acid (F-LA) was added to 150ml culture solution consisting of 75ml strained rumen fluid and 75ml McDougall's artificial saliva. Culture solution for incubation was also made without malate, fumarate, and C18:2 (control). Two grams of feed consisting of 1.4g concentrate and 0.6g ground alfalfa (DM basis) was also added to the culture solution of each treatment. An in vitro incubation in batch was made anaerobically in a shaking incubator for up to 12h at 39°C. The pH of the culture solution was increased (P<0.0001) in M-LA or F-LA treatments from 3h to 12h compared with the control and LA treatments. At 12h incubation, the concentration of total VFA in the culture solution was higher (P<0.01) in M-LA and F-LA than in control and LA treatments. Concentration of C3 by M-LA and F-LA was increased at 3h (P<0.01), 6h (P<0.01) and 12h (P<0.01) compared with control and LA. However, no difference in C3 concentration was observed between control and LA, or between M-LA and F-LA. Accumulated total gas produced for up to 12h incubation was increased (P<0.01) by M-LA or F-LA compared with the control. Accumulated total methane produced for up to 12h incubation, however, was greatly reduced (P<0.01) by all the supplements compared with control, and its production from M-LA or F-LA was smaller than the LA. The M-LA or F-LA also increased (P<0.05-<0.001) the concentrations of cis9, trans11-CLA for all incubation times and trans10, cis12-CLA at 1h (P<0.01), 3h (P<0.05), and 12h (P<0.05) incubation times compared with LA. It can be concluded that malate and fumarate, as propionate precursors, act as alternative electron sinks and may compete with CH4 generation and bio-hydrogenation of C18:2 in the utilization of metabolic H2. The highest CLA concentration at the early incubation stage (1h) was accompanied by reduced propionate proportion. Linoleic acid is also considered one of the potential alternatives to suppress CH4 generation.