Effects of mineral or protein-energy supplementation and genetic group on metabolism parameters of young beef bulls grazing tropical grass during the rainy season

•Protein-energy supplementation to grazing beef bulls was effective to maximize ruminal fermentation during the rainy season.•Senepol animals showed a lower acetate:propionate ratio; and when fed protein-energy supplement, a greater relative abundance of prevotella sp., S. bovis and S. ruminantium was observed.•Nellore animals had an increase in the relative abundance of total Archaea, F. succinogenes (when protein-energy supplemented) and R. albus (when mineral supplemented).