Effect of a Blend of Phytogenic Compounds Addition on Rumen Microbiota and Nitrogen Utilization Efficiency during the Supplementation of Grazing Nellore Cattle

The objective of this study was to evaluate the effect of the addition of a phytogenic compounds blend (PHA) containing hydrolyzable tannins, carvacrol and cinnamaldehyde oil in the mineral salt or energy supplement on the rumen microbiota and nitrogen metabolism of grazing Nellore cattle. Eight castrated Nellore steers were distributed in a double Latin square 4 × 4 design, with a 2 × 2 factorial arrangement (two type supplements and the addition or not of PHA) as follows: energy supplement without PHA addition (EW); energy supplement with PHA addition (EPHA); mineral supplement without the addition of PHA (MW); and mineral supplement with PHA addition (MPHA). Steers that received supplements with PHA have a lower ruminal proportion of Valerate (with PHA 1.06%; without PHA 1.15%), a lower ruminal abundance of Verrucomicrobia and a tendency for lower DM digestibility (with PHA 62.8%; without PHA 64.8%). Energy supplements allowed higher ammonia concentrations (+2.28 mg of NH3-N/dL), increased the propionate proportion (+0.29% of total VFA), and showed a tendency to have a higher abundance of Bacteroidetes and a lower abundance of Firmicutes in the rumen. The PHA addition in the supplement did not improve the use of nitrogen in grazing cattle, but negatively affected the diet digestibility.