The Impact of Mineral and Energy Supplementation and Phytogenic Compounds on Rumen Microbial Diversity and Nitrogen Utilization in Grazing Beef Cattle

Abstract

The objective of this study was to evaluate the effect of the addition of a phytogenic compound blend (PHA) containing hydrolyzable tannins, carvacrol, and cinnamaldehyde oil to mineral salt or energy supplementation 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 types of supplements with or without the addition of the PHA), as follows: energy supplement without the PHA addition (EW); energy supplement with the PHA addition (EPHA); mineral supplement without the addition of the PHA (MW); mineral supplement with the PHA addition (MPHA). Steers that received supplements with the PHA have a lower ruminal proportion of valerate (with the PHA, 1.06%; without the PHA, 1.15%), a lower ruminal abundance of Verrucomicrobia, and a tendency for lower DM digestibility (with the PHA, 62.8%; without the PHA, 64.8%). Energy supplements allowed for higher ammonia concentrations (+2.28 mg of NH₃-N/dL), increased the propionate proportion (+0.29% of total VFA), and had a higher ruminal abundance of Proteobacteria and Spirochaetae phyla in the rumen. The PHA addition in the supplement did not improve nitrogen retention, reduced the ruminal proportion of valerate, and had a negative impact on both the total dry-matter digestibility and the abundance of several ruminal bacterial groups belonging to the Firmicutes and Verrucomicrobia phyla.

Keywords: digestibility; essential oils; hydrolyzable tannins; rumen fermentation; ruminal bacteria.

Figure 1

Interaction effect of type of supplement × time after supplementation on the ruminal proportion of acetate (p < 0.001), butyrate (p < 0.001), valerate (p < 0.001), and isovalerate (p = 0.008) in Nellore cattle grazing Urochloa brizantha cv. Marandu supplemented with energy supplements or mineral supplements.

Figure 2

Beta-diversity Bray–Curtis index computed for nonparametric statistical tests between rumen microbial communities of Nellore cattle grazing Urochloa brizantha cv. Marandu and supplemented with energy supplements (SEs) or mineral supplements (SMs). There were no observed effects of the addition of a phytogenic compound blend containing 10% of carvacrol and cinnamaldehyde oil, and 90% hydrolyzable tannins extracted from berries and grapes at a dose of 1.5 g/kg of ingested dry matter.

Figure 3

Relative abundance of operational taxonomic units (OTUs) classified at family (A) and genera level of ruminal Archaea (B) and bacteria (C) domain in Nellore cattle grazing Urochloa brizantha cv. Marandu during the rainy season influencing by the supplementation with energy supplement without phytogenic compounds addition (EW), energy supplement with the phytogenic compound addition (EPHA), mineral supplement without the phytogenic compound addition (MW), or mineral supplement with the phytogenic compound addition (MPHA). Only the taxa with significative (p < 0.05) or tendencies (p < 0.10) values are shown.