Background The use of synthetic compounds as growth promoters in animal production, is now limited or even banned by health agencies globally due to human safety concerns. In feedlot cattle, when using high grain diets, it is necessary to supplement the diet with compounds capable of modulating the rumen in order to reduce the incidence of acidosis and improve growth. In this context, natural substances have become promising substitutes. The objective of this study was to evaluate the effects of a natural additive blend (NA) on animal performance, the rumen microbiome and ingestive behavior in 40 young bulls.Results The initial and final average body weight was similar (P > 0.05) for all diets, although average daily gain increased linearly (P < 0.01) when NA was fed. However, feed efficiency improved linearly (P < 0.05) by including NA in the diet. Principal volatile fatty acid: acetic, butyric, isovaleric and valeric decreased linearly (P < 0.02) following NA addition. Similarly, NA addition linearly decreased (P < 0.02) the acetate/propionate ratio. The propionate and isobutyric acid concentrations showed a positive quadratic effect (P < 0.05). Furthermore, NA addition reduced ammonia concentrations (P < 0.001) and ruminal pH was not affected (P > 0.05) by the diets. The rumen microbiome was significantly different between beef cattle fed the different treatments (P < 0.05), with a reduction in the archaea, and within the Clostridium, Robinsoniella, Acidaminococcus, Acetitomaculum, Succinimonas and Weissella (P < 0.05) seen when NA was fed. The functional capacity of the rumen microbiome was affected following NA supplementation. Overall, we observed Aldehyde oxidase/xanthine dehydrogenase, molybdopterin binding; RecG, N-terminal antiparallel four helix bundle; Transposase, ISC1217; Restriction endonuclease, type II, XamI; Acyl-protein synthetase, LuxE; ABC-2 transporter; which could be related to the natural additives mechanism of action.Conclusions Animal performance was improved in a dose-dependent manner by natural additive addition to the diet of bulls. These beneficial effects are correlated to changes in the rumen microbiome. Our findings suggest that the natural additive blend used in this study could be used as an alternative natural substitute to synthetic antibiotics for animal production.