Endo-1,3-β-D-glucanase activity influences in vitro ruminal fermentation of diets varying in forage:concentrate.

With growing concerns to reduce global methane emissions, there is a pressing need to explore alternative strategies to mitigate methane production in ruminant livestock species. The objectives of this study were to evaluate the effects of increasing dosage of endo-1,3-β-D-glucanase on in vitro ruminal fermentation from diets varying in forage:concentrate. Ruminal contents were obtained from 2 ruminally cannulated Angus × Holstein steers. The experimental design was a randomized complete block design with a 3 × 6 factorial arrangement of treatments. The basal substrates (DM basis) were high-forage (90% tall fescue hay, 10% corn; 90F:10C), equal forage:concentrate (50% tall fescue hay, 50% corn; 50F:50C), or high-concentrate (90% corn, 10% tall fescue hay; 10F:90C). Six doses of endo-1,3-β-D-glucanase were tested: 0, 5, 10, 25, 50, and 100 units/100 mL of ruminal inoculum. Recombinant endo-1,3-β-D-glucanase was diluted to working concentrations with 100 mM sodium acetate buffer, and then working solutions (1 mL) were added to fermentation vessels immediately before inoculum addition. Substrates were added to fermentation vessels and incubated for 48 h. There were 2 technical replicates per treatment in each run, and 3 runs to constitute the experiment. Results were analyzed with the GLM procedure of SAS. Increasing dosage of endo-1,3-β-D-glucanase did not influence (P ≥ 0.10) the rate of gas production or cumulative methane production. Cumulative gas production (mL, mL/g substrate, and mL/g substrate digested) increased linearly (P ≤ 0.03) with increasing endo-1,3-β-D-glucanase activity. Microbial biomass, true dry matter (DM) digestibility, apparent DM digestibility, and neutral detergent fiber digestibility were not influenced (P ≥ 0.21) by increasing endo-1,3-β-D-glucanase dose. The molar acetate proportion and acetate:propionate decreased linearly (P < 0.001) with increasing endo-1,3-β-D-glucanase activity. The molar propionate, butyrate, and valerate proportions in the fermentation media linearly increased (P < 0.001) with increasing endo-1,3-β-D-glucanase activity. Decreasing forage:concentrate decreased (P < 0.05) gas and methane production per gram of substrate digested and increased (P < 0.001) digestibility and total short-chain fatty acid (SCFA) concentration. These data demonstrate that endo-1,3-β-D-glucanase modulates in vitro ruminal fermentation of diets varying in forage:concentrate by altering molar SCFA proportions.