A preliminary study on the effects of red Bonnemaisonia hamifera seaweed on methane emissions from dairy cows

The red seaweed Bonnemaisonia hamifera has shown potential as a CH₄-mitigating feed additive in vitro, and hence, this pilot study aimed to investigate the potential of the seaweed when fed to dairy cows. The study was conducted as a 4 × 4 Latin square using 4 Danish Holstein cows with 4 periods of 7 d where the cows were placed in respiration chambers for the last 3 d. Milk yield and feed intake were recorded daily. The cows were fed a TMR without B. hamifera (control) or the same diet with the addition of, on a DM basis, 0.33% (low), 0.66% (medium), and 1% (high) B. hamifera. Increasing inclusion levels of B. hamifera linearly decreased CH₄ emissions with up to a 13.3% reduction in daily CH₄ production (g/d), 15.7% reduction in CH₄ yield (g/kg DMI), and 16.4% reduction in CH₄ intensity (g/kg ECM). In contrast, linear increases were observed in daily H₂ production (g/d), H₂ yield (g/kg DMI), and H₂ intensity (g/kg ECM). The exact nature of the antimethanogenic compounds in B. hamifera is unknown; however, the concentration of the potentially harmful compound, bromoform, was remarkably lower in B. hamifera compared with reported concentrations in the known antimethanogenic red seaweed Asparagopsis taxiformis. In conclusion, B. hamifera showed CH₄-mitigating properties in this preliminary study, but further in vivo studies are needed to fully evaluate the potential of the seaweed as an antimethanogenic feed additive.