Effects of different feeding regimes on growth performance, antioxidant activity, rumen fermentation, rumen microbiota and rumen metabolism in beef cattle

The feeding regime significantly impacts on the production performance, ruminal fluid microbiota, and metabolites of ruminants. However, studies comparing the microbial metagenomics and metabolites in ruminal fluid of beef cattle fed pasture-based grazing and housed total mixed ration (TMR) feeding regimes have rarely been reported. Forty healthy Guanling beef cattle were divided into two equal groups according to a randomized complete block design. The pasture-based grazing group (BG) was allowed to the grazing period was 08:00–18:00 at a natural ranch. The housed TMR feeding group (BB) was reared under a housed feeding system and fed a TMR diet. Each treatment consisted of 20 beef cattle, and the experimental period lasted for 90 d. The metagenomics and metabolomics were used analysis ruminal fluid microbiota and metabolism. The results indicated that the BB group showed significantly higher levels of average daily gain, total antioxidant capacity, catalase, 2,2-diphenyl-1-picrylhydrazyl scavenging activity, ammonia nitrogen, and volatile fatty acid ( P < 0.05), whereas it had significantly lower levels of malondialdehyde and hydroxyl free radical relative to the BG group ( P < 0.05). Compared with the BB group, the BG group exhibited a significantly increased ( P < 0.05) abundance of Bacillota at the phylum level but a significantly decreased ( P < 0.05) abundance of Prevotella at the genus level. The modules associated with these relative abundance levels (Reductive citrate cycle (Arnon-Buchanan cycle), and Guanine ribonucleotide degradation, GMP = > Urate) were significantly more important in the BG group ( P < 0.05) than in the BB group. Glycosyltransferase 2_Glycos_transf_2 was significantly enriched in the BB group, whereas glycoside hydrolase (GH)3, GH78, and GH36 were significantly enriched in the BG group. Metabolomic analysis revealed that linoleic acid metabolism was the dominant pathway in the rumen. Overall, the housed TMR-fed cattle enhanced growth performance, antioxidant activity, rumen fermentation, and Prevotella abundance, whereas the pasture-based grazing fed cattle enhanced Bacillota abundance and linoleic acid metabolism.