Abstract
Abstract The study was carried out to evaluate the effect of tannins extract (TN) associated to two levels of urea in the supplement of grazing beef cattle on ruminal bacterial abundance. Were used eight rumen cannulated Nellore steers (293 kg ± 5.6 BW) in a double Latin square 4 x 4 (four periods of 28 each and four supplements: LU = low urea without TN; LUT = low urea plus TN; HU = high urea without TN and HUT = high urea plus TN). Steers grazing Urochloa brizantha cv. Marandu and were supplemented at 3 g/kg BW cwith soybean meal, corn, mineral mix and two levels of urea (3% or 5%) associated or not to TN (SilvaFeed-ByPro at 0.7 g / kg). Samples of ruminal content were collected after supplementation (+ 3h), V3/V4 regions of 16SrRNA gene was sequencing using the Illumina MiSeq. Quantitative Insights into Microbial Ecology (QIIME v.1.9.1) were used to filter reads and determine Operational Taxonomic Units (OTUs). DESeq2 differential abundance analysis were performed using each steer on LU supplement as own control on others supplements and evaluated by Kruskal-Wallis rank sum test considering statistical significance at P < 0.10. Only 5 OTUs differed significantly between treatments. Enterorhabdus.spp population were less abundant in HU, but TN was able to reduce the abundance in both LUT and HUT(P = 0.049). The ruminal abundance of Streptococcus.spp (P = 0.026), Fusobacterium.spp (P = 0.053) and Synergistes.spp (P = 0.048) was reduced by TN, but had no effect of urea level. Enterorhabdus.spp, Streptococcus.spp and Fusobacterium.spp are associated with inflammatory bowel diseases, ruminal acidosis and to liver abscesses in cattle, respectively. Betaproteobacteria class were less abundant in HU treatment (P = 0.048), this heterogeneous class bacterial content some nitrogen fixing bacteria and some pathogens important in plants and animals. In conclusion, TN reduced the ruminal population of important ruminal pathogens bacterial.
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