Regulatory effects of high concentrate diet synergistically fermented with cellulase and lactic acid bacteria: In vitro ruminal fermentation, methane production, and rumen microbiome

Abstract

This study aimed to investigate, using in vitro technique and high-throughput sequencing, the regulatory effect of fermented total mixed ration (FTMR) prepared using synergistic fermentation of lactic acid bacteria (LABs) and cellulase on rumen fermentation, methane emission, and rumen microbiome. The concentrate-to-forage ratio of the TMR was 6: 4, net energy was 1.66 Mcal (for lactating cows), and metabolizable energy and protein allowable milk yield predictions were 36.3 kg or 37.6 kg from Cornell-Penn-Miner dairy model (CPM dairy). The LABs (10⁶ colony-forming units (cfu)/g, Lactobacillus buchneri and Lactobacillus plantarum, at a ratio 1:1) and 1 g fibrolytic enzyme (10,000 U/g activity) per fresh matter were used for ensiling the TMR. The results show that the synergistic fermentation of cellulase and lactic acid bacteria reduces the proportions of structural carbohydrate, neutral detergent insoluble protein, and acid detergent insoluble protein in high concentrate diet while increasing the proportions of crude protein, soluble protein, and non-protein nitrogen. The FTMR with LABs and cellulase addition diet had higher ammonia nitrogen, acetic acid, lactic acid contents, and lower pH than TMR. Also, the in situ effective degradation rate of neutral detergent fiber, dry matter, and crude protein was elevated. At the same time, the abundance of lactic acid bacteria was improved when LABs and cellulase were added to FTMR. The in vitro experiments showed that synergistic fermentation increased the proportion of propionic acid (26.47 vs 22.39, P = 0.0166) and ammonia nitrogen concentration (12.25 vs 10.24, P = 0.0144) and reduced ruminal pH (6.56 vs 6.68, P = 0.0249). In addition, the proportion of acetic acid (60.34 vs 66.38, P = 0.0059) and the ratio of acetic acid to propionic acid concentration (2.29 vs 2.97, P = 0.0077) was lowered when FTMR was prepared by LABs and cellulase addition. Fermented total mixed ration with LABs and cellulase changed the rumen fermentation pattern and reduced methane production (184.33 ml vs 219.38 ml, P = 0.0003) by regulating in vitro ruminal bacteria's abundance and the diversity of protozoa and methanogens. Therefore, for a high-concentrate diet, adopting a fermented total mixed ration technology with LABs and cellulase addition is a clean option that could help reduce greenhouse gas production and protect the environment.