PSXII-26 - Effect of different supplements plus phytogenic additives on ruminal bacterial community of grazing beef cattle

Abstract: Changes in ruminal microbial community can affect animal productivity, nutrient utilization efficiency, and environmental impact. This study aimed to evaluate the effect of two levels of supplementation plus a blend of phytogenic additives (essential oils, saponins, and spices) on the ruminal bacterial community in beef cattle grazing tropical pastures. The experiment was conducted at the Beef Cattle Sector of UNESP, Jaboticabal-BR, and lasted 84 days. Nine castrated Nellore steers (body weight of 262 ± 31.2 kg) cannulated in the rumen were assigned to 3 simultaneous 3 × 3 Latin square designs. Animals were kept on pasture of Urochloa brizantha cv. Marandu during the rainy season. The treatments included ad libitum mineral supplementation (MS) as the control group, added mineral supplementation of 0.1% of body weight per day plus Cargill® phytogenic blend (AMSP), and energetic-protein supplementation, 0.3% of body weight per day plus Cargill® phytogenic blend (EPSP). Ruminal samples were collected on day 26 of each experimental period. A mix of liquid and solid rumen content (6 mL) was taken before supplementation and immediately frozen in liquid nitrogen. Total genomic DNA was extracted using the Quick-DNA™ Fecal/Soil Microbe kit. The V3-V4 hypervariable regions of the bacterial 16S rRNA gene were amplified using universal primers 341F and 806R. The PCR fragments were submitted to sequencing on an Illumina NovaSeq 6000 PE 250 platform. The sequences were processed using mothur, grouped into operational taxonomic units (OTUs) using a similarity cut-off value of 97%, and the bacterial OTUs were classified using the SILVA database. Bacterial community composition was compared between treatments using a Kruskal–Wallis test and Wilcoxon’s post-hoc test using Rstudio. A total of 27 phyla, 224 families, and 577 genera were assigned by the taxonomic analysis of the ruminal bacterial community. The phyla Bacteroidetes (44.45±9.43) and Firmicutes (42.50±7.18) represent over 86% of the total relative abundance in the rumen of Nellore steers and were not influenced by the supplementation (P≥0.250). The relative abundances of the Spirochaetes phylum, Spirochaetaceae family, and Treponema genus decreased in the rumen of AMSP supplemented animals (P≤0.037) and were similar between MS and EPSP. Additionally, the EPSP supplementation resulted in decreased relative abundances of TM7, TM7 family incertae sedis, and TM7 genus incertae sedis relative abundances compared to those in MS (P=0.031) but not between AMSP and EPSP supplementations. The addition of phytotherapy blend in the supplements led to decreased SR1, SR1 family incertae sedis, and SR1 genus incertae sedis abundances in the rumen (P≤0.012). This study indicates that the relative abundance of the dominant phyla was not affected by the supplementation levels, but the addition of the phytogenic blend in the supplement decreased the relative abundances of specific bacterial phyla, families, and genera,