Farming ruminants contributes to over 25% of anthropogenic methane (CH4), a compound which is 25 times stronger at heat trapping than CO2, making it one of the most impactful of greenhouse gases. Because of this, mitigation of CH4 emissions is critical both environmentally and agriculturally. In this study, the effects of an approved feed additive, Red Lake Earth (RLE), on cattle rumen fluid methane production was observed in vitro. Pure diatomaceous earth (DE), pure calcium bentonite, and mined RLE containing a mixture of these two materials, were tested for their effects on CH4 production in vitro at concentrations from 20 to 100 g/L. After 24 hours of incubation, CH4 production was measured directly from culture headspace using gas chromatography. RLE treatments were found to reduce CH4 production by 90.5% ± 1.9 % compared to untreated cultures, and the 20 g/L treatment was selected for 5 day time course studies using rumen fluid from 4 independent animals. Methane production in RLE treated, 5-day cultures was, on average, inhibited by 59% ± 11% compared to untreated controls. Liquid culture samples were analyzed using quantitative real time PCR (qPCR; mcrA, 18S and 16S rDNA) and reverse transcriptase qPCR (mcrA) to quantify the effects of RLE on numbers of protozoa, bacteria and archaea in cultures. No significant changes in total archaea, bacteria, mcrA genes or protozoa were found when cultures were treated with RLE. However, there was a significant reduction in the transcript to gene ratio of the mcrA gene suggesting that RLE may inhibit methanogenesis by indirectly reducing transcriptional activity. This research strongly supports the ability of RLE to reduce rumen CH4 production in vitro by reducing methanogen activity and suggests further genomic and in vivo studies to assess the potential impact of RLE as a feed additive.
