Effects of rare earth element lanthanum on rumen methane and volatile fatty acid production and microbial flora in vitro

The objectives of the trial were to study the effects of rare earth element (REE) lanthanum (La) on the in vitro rumen methane (CH4) and volatile fatty acid (VFA) production and the microbial flora of feeds. Four feed mixtures with different levels of neutral detergent fibre (NDF), that is 20.0% (I), 31.0% (II), 41.9% (III) and 52.7% (IV), were formulated as substrates. Five levels of LaCl3, that is 0, 0.4, 0.6, 0.8 and 1.0mmol/kg dry matter (DM), were added to the feed mixtures, respectively, as experimental treatments in a two-factor 5x4 randomized design. The in vitro incubation lasted for 24h. The results showed that supplementing LaCl3 increased the total gas (p<0.001) production and tended to increase the total VFA production (p=0.072) and decreased the CH4 production (p=0.001) and the ratios of acetate/propionate (p=0.019) and CH4/total VFA (p<0.001). Interactions between LaCl3 and NDF were significant in total gas production (p=0.030) and tended to be significant in CH4 production (p=0.071). Supplementing LaCl3 at the level of 0.8mmol/g DM decreased the relative abundance of methanogens and protozoa in the total bacterial 16S rDNA analysed using the real-time PCR (p<0.0001), increased F.succinogenes (p=0.0003) and decreased R.flavefaciens (p<0.0001) whereas did not affect R.albus and anaerobic fungi (p>0.05). It was concluded that LaCl3 decreased the CH4 production without negatively affecting feed digestion through manipulating rumen microbial flora when feed mixtures with different levels of NDF were used as substrates.