Effect of α‐cyclodextrin‐allyl isothiocyanate on ruminal microbial methane production in vitro

The objective of the present study was to investigate the effects of α-cyclodextrin-allyl isothiocyanate (CD-AI) on ruminal microbial methane production and rumen fermentation of corn starch, soluble potato starch or hay plus concentrate (1.5:1) by mixed rumen microorganisms. Diluted rumen fluid (30 mL) was incubated anaerobically at 38°C for 6 and 24 h with or without CD-AI (0, 0.4, 0.8, 1.6 and 3.2 g/L). The pH of the medium was unchanged by CD-AI in all substrates. The molar proportion of acetate was decreased and propionate was increased with a corresponding decrease in acetate : propionate ratio (P < 0.05). Total volatile fatty acids and butyrate were increased (P < 0.05). Ammonia-N was decreased (P < 0.05). Except with soluble potato starch, numbers of protozoa were unchanged after 6 h. As concentration of CD-AI increased from 0 to 3.2 g/L, fermentation of corn starch, soluble potato starch and hay plus concentrate resulted in decreased (P < 0.05) methane production of 49–100% (6 h) and 14–100% (24 h); 39–100% (6 h) and 16–100% (24 h); and 45–100% (6 h) and 17–100% (24 h), respectively. When hay plus concentrate was used as substrate, methanogenic bacteria were decreased (P < 0.05) with 0.8 g/L of CD-AI after 6 h. Excluding the lower dose level (0.4 g/L) of CD-AI, digestibility of neutral detergent fiber of hay plus concentrate was decreased (P < 0.05) after 24 h. A suitable level of CD-AI could therefore be used as a supplement to inhibit methane production and improve rumen fermentation without detrimental effects on fiber digestion.