The anti-methanogenic efficacy of Asparagopsis taxiformis: Could it be attributable solely to its bromoform content?

The seaweed Aspragopsis taxiformis has been shown to be a successful intervention to mitigate methane (CH₄) emissions from ruminants due to the content of halogenated components, including bromoform. Some groups have been exploring extracting or synthesizing bromoform to be used as a feed additive rather than using whole seaweed biomass. This study was conducted to understand the differences between whole A. taxiformis biomass and bromoform in their ability to reduce CH₄ production when included in ruminant diets. A series of in vitro experiments were conducted, with a control group consisting of a 50 % hay:50 % concentrate. A. taxiformis biomass supplementation levels of 0.25 and 0.50 %, containing 0.0037 and 0.0077 mg bromoform on a dry matter (DM) basis, respectively, were evaluated. Bromoform was evaluated at 0.0018, 0.0036, and 0.0073 mg. The two highest levels of bromoform were comparable to the bromoform content in the seaweed biomass. Adding A. taxiformis biomass led to significant reductions in CH₄ yield (mL/g) of 62.5 and 95.6 %, respectively, without compromising in vitro fermentation characteristics. The addition of bromoform resulted in a decrease in the CH₄ yield (mL/g) by 7.6, 23.0, and 59.6 %, respectively. In conclusion, while bromoform led to a dose-dependent reduction in CH₄ production, A. taxiformis has a greater effect at equivalent doses of bromoform, suggesting that the other components in the biomass, which were responsible for up to 40 % of the reduction, play a significant role in the anti-methanogenic efficiency of A. taxiformis.