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Antibiotics are extensively fed to beef cattle as they act as rumen modulators, improving animal efficiency and decreasing methane emissions. However, current recommendations by health agencies to limit/ban antibiotic use in animal production call for alternatives such as natural additives. In this study, we aimed to evaluate the efficacy of natural additives in methane mitigation. Bulls (½Angus and ½Nellore) 16±2.2 months old, with average body weight of 385±20.7 kg were fed a basal diet (70 % concentrate, 30 % corn silage) offered ad libitum for 62 days in a feedlot and randomised on five treatments (8 bulls/treatment): control treatment, and addition of 1.5, 3.0, 4.5, or 6.0 g/day/animal of a blend of natural additives containing 37.5 % each of clove essential oil, the commercial blend containing vanillin, eugenol and thymol, 12.5 % and 12.5 % of castor and cashew oils). Methane production from rumen fluid was estimated based on the theoretical fermentation balance for observed molar distribution of VFAs in the rumen. DNA extracted from rumen fluid were sequenced and analysed for methane genes within the MG-RAST database. The natural additives linearly reduced methane production (76 %, P<0.02). Evaluation of Archaeaabundance showed a reduction (79 %, P<0.05) in the major methane producing genera: Halorhabdus, Ferroplasma, Methanoplanus, Picrophilus. A reduction of Fibrobacter and Lactobacillus (71 %), the greatest producers of acetate releasing hydrogen for methane formation was also observed. Our findings suggest that natural additives such as essential oils may be useful in the mitigation of greenhouse gases such as methane in animal production.