In vitro dose-response of bromoform stabilized in vegetable oil on rumen fermentation and methane production

Synthetically manufactured bromoform may provide a sustainable and economically viable alternative to macroalgae harvesting and cultivation for mitigating methane emissions in ruminants. Our objective was to evaluate the effect of varying doses of synthetic bromoform stabilized in vegetable oil on rumen fermentation, digestibility, and methane production using an in vitro batch culture system. Four treatments were evaluated: 0 (BR0), 1,000 (BR1), 2,500 (BR2), and 5,000 (BR5) mg bromoform/kg oil, added to batch culture vessels at a 2% DM basis. A randomized complete block design was applied across 3 periods, with incubations conducted for 3, 6, 12, 24, and 72 h in each period. Treatments were replicated 3 times at each incubation time. At 72 h, methane (mg/g of disappeared DM) was reduced by 32.3%, 96.4%, and 100% in BR1, BR2, and BR5, respectively, compared with BR0. The inclusion of bromoform at varying doses did not influence fermentation medium pH or apparent substrate disappearance, as measured by DM, NDF, and ADF disappearance. Bromoform inclusion modified the ruminal VFA profile. At 12 h, BR2 and BR5 treatments exhibited decreased acetate concentrations relative to BR1, whereas at 24 h, these treatments had reduced acetate concentrations compared with BR0. Moreover, by 72 h, BR5 had the lowest acetate concentrations among treatments. The acetate-to-propionate ratio was lesser in BR5 and marginally lesser in BR2 compared with BR0. Butyrate concentration was greater in BR1 and BR5 compared with BR0. At 72 h, BR2 and BR5 showed greater concentrations of valerate and caproate concomitant with a decrease in isobutyrate concentrations relative to BR0 and BR1. Isovalerate and 2-methylbutyrate concentrations were greater in BR1 compared with BR2 and BR5. The collective findings of this study indicate that synthetic bromoform inclusion (BR2 and BR5) markedly reduced methane production, preserved digestibility, and altered rumen fermentation characteristics, suggesting a compensatory shift in reducing equivalents utilization by the rumen microbiota.