Effects of cashew nut-shell extract and monensin on in vitro ruminal fermentation, methane production, and ruminal bacterial community

The objective of this study was to evaluate the effects of cashew nut-shell extract (CNSE) and monensin on ruminal in vitro fermentation, CH4 production, and ruminal bacterial community structure. Treatments were: control (CON, basal diet without additives); 2.5 μM monensin (MON); 100 ppm CNSE granule (CNSE100); and 200 ppm CNSE granule (CNSE200); each incubated with 52 mL buffered ruminal content and 500 mg of total mixed ration for 24 h using serum vials. The experiment was done as a complete randomized block design with 3 runs. Run was used as a blocking factor. Each treatment had 5 replicates, in which 2 were used to determine nutrient degradability, and 3 were used to determine pH, NH3-N, volatile fatty acids, lactate, total gas, CH4 production, and bacterial community composition. Treatment responses for all data, excluding bacterial abundance, were analyzed with the GLIMMIX procedure of SAS. Treatment responses for bacterial community structure were analyzed with the PERMANOVA test ran with the R Vegan package. Orthogonal contrasts were used to test the effects of (1) ADD-(CON vs. MON, CNSE100, and CNSE200); (2) MCN-(MON vs. CNSE100 and CNSE200); and (3) DOSE-(CNSE100 vs. CNSE200). Significance was declared at P ≤ 0.05 and tendencies at 0.05 < P ≤ 0.10. We observed that pH, acetate, and acetate:propionate ratio in the CNSE100 treatment were lower compared with CNSE200, propionate in the CNSE100 treatment was greater compared with CNSE200. Compared with MON, CNSE treatments tended to decrease total lactate concentration. Total gas production of CON was greater by 2.63% compared with all treatments and total CH4 production was reduced by 10.64% in both CNSE treatments compared with MON. Also, compared with MON, in vitro dry matter degradability in CNSE treatments were lower. No effects were observed for NH3-N, and in vitro neutral detergent fiber degradability. Lastly, the relative abundances of Prevotella, Treponema, and Schwartzia were lower, while the relative abundances of Butyrivibrio, and Succinivibrio were greater in all treatments compared with CON. Overall, the inclusion of CNSE decreased CH4 production compared with MON, making CNSE a possible CH4 mitigation additive in dairy cattle diets.