PSVI-4 Effects of exogenous fibrolytic enzymes on beef cattle fed growing diets: Ruminal microbiome

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Abstract The effect of pre-treatment with fibrolytic enzymes [cellulase/xylanase (Trichoderma ressie)] of growing diets (high quality and low-quality) on ruminal microbiome relative abundance (RA) were evaluated. Ruminally cannulated beef steers (n = 5; BW = 520 ± 30 kg) were used in a 5×4 unbalanced Latin square design using a 2×2 factorial arrangement of treatments: (a) growing diet quality [high (HQ) and low (LQ)] and (b) enzyme inclusion (0 or 0.75 mL/kg of diet DM). Steers were individually fed ad libitum throughout four 21-d periods consisting of 14-d of adaptation and 7-d of collections. Ruminal fluid samples (100 mL) were collected on d-5 of each collection-period, at 6 h post feeding for DNA extraction and determination of microbial RA. Microbiome data were sequenced by Illumnia® NovaSeq™ 6000 (16S rRNA). Regardless of enzyme×diet quality interaction (P ≥ 0.11) or pre-treatment with enzyme (P ≥ 0.12), Domain RA was affected (P ≤ 0.04), in which LQ diets increased RA of Bacteria (93.25 vs. 86.80%) and decreased Archaea (6.75 vs. 13.20%). In Phylum, LQ diets decreased RA (P ≤ 0.04) of Euryarchaeota (6.75 vs. 13.21%), and increased Bacteroidetes (11.22 vs. 2.26%). Within Class, LQ diets decreased RA (P ≤ 0.04) of Clostridia (38.66 vs. 51.40%), Methanobacteria (6.75 vs. 13.21%), and increased Bacteroidia (10.62 and 1.47%). Within Order LQ diets, decreased RA (P ≤ 0.04) of Clostridiales (38.47 vs. 51.29%), Methanobacteriales (6.75 vs. 13.21%), and increased Bacteroidales (10.62 vs. 1.47%). In Family, LQ diets showed decreased RA (P ≤ 0.04) of Methanobacteriaceae (6.75 vs. 13.21%), Ruminococcaceae (6.71 vs. 2.18%), and increased Prevotellaceae (9.83 vs. 1.17%). In Genus, LQ diets showed increased RA (P ≤ 0.03) of Prevotella (9.61 vs. 1.10%). The dietary pre-treatment with fibrolytic enzymes seems to not dramatically affect RA of ruminal microbiome, while growing diet quality greatly influenced ruminal microbiome RA.