Dose-dependent inhibitory effects of an investigational feed additive containing bromoform on methane emissions from cattle fed fresh pasture

Bromoform, a bioactive compound in certain seaweeds, has gained attention for its methane-mitigating effects in ruminants. Research is underway to use synthetic bromoform as an alternative for providing consistent and predictable dosing of the bioactive compound, but its inherent volatility and liquid form limit its application. To address these challenges, an investigational feed additive (IFA) in the form of a powder containing synthetic bromoform has been developed by Rumin8 Pty Ltd., West Perth, WA, Australia. The objective of this study was to evaluate the effect of the Rumin8 IFA on methane emissions from cattle fed fresh pasture. Sixteen 18-month-old Hereford × Friesian heifers (427 ± 11 kg; mean ± SD) were stratified by weight and randomly allocated to control and treatment groups using a randomised block design. Treatments included IFA doses at 100, 300, or 500 mg/d of bromoform per heifer, plus a placebo control. The heifers were fed fresh pasture twice daily with a total feed allowance set at a level of 1.6 to 1.8 times their maintenance energy requirements with 800 g of dried distiller's grain pellets containing treatments or placebo before each meal. After 16 d, the heifers' methane emissions were measured in open-circuit respiration chambers for 48 h. The results showed that pasture-fed heifers produced less methane when treated with the bromoform-containing IFA at every dose level (<i>P</i> < 0.05). Reductions of up to 50% in methane emissions were observed in the first 4 h after feeding (<i>P</i> < 0.05). Methane yield declined linearly with bromoform dose (<i>P</i> = 0.001), showing 16% (300 mg) and 24% (500 mg) reductions vs. control (<i>P</i> < 0.05). No treatment effect on feed intake or bromoform accumulation in muscle or fat was observed. In summary, the IFA containing synthetic bromoform significantly reduced methane emissions in pasture-fed heifers, with a clear dose-response relationship, no adverse effect on feed intake, and no detectable residues in muscle or fat. These results have significant implications for reducing the environmental impact of cattle production, offering a practical solution to the challenge of methane emissions in pasture-fed systems where animals have access to supplements.