A meta-analysis of effects of seaweed and other bromoform-containing feed ingredients on methane production, yield, and intensity in cattle

Methane (CH 4 ) emissions from ruminants contribute significantly to global GHG emissions. Bromoform (CHBr 3 )-containing feed ingredients, such as Asparagopsis seaweed, have emerged as promising tools to reduce enteric CH 4 emissions. This meta-analysis quantitatively assessed the effects of CHBr 3 -containing seaweeds and synthetic CHBr 3 -based additives on CH 4 production (g/d), CH 4 yield (g/kg DMI), and DMI, as well as CH 4 intensity (g/kg product) and production (milk or daily gain in dairy and beef cattle, respectively). Data were collected from 14 studies, with 39 treatment mean differences for CH 4 production, comprising both beef and dairy cattle fed CHBr 3 -containing ingredients, while accounting for dose, DMI, and diet composition. The random-effects model's estimates revealed that at an average CHBr 3 dose of ≈28.3 mg/kg DM, CH 4 production was reduced by 47.3%, CH 4 yield by 43.3%, and CH 4 intensity by 39.0%, with increases in the CHBr 3 dose resulting in larger efficacy in mitigating CH 4 emissions. The efficacy of CHBr 3 was influenced by cattle type, with greater mitigation effects in beef cattle than dairy catle, and by dietary composition, with greater reductions observed in diets higher in starch, whereas higher NDF levels attenuated the effect of CHBr 3 . At the average CHBr 3 dose, estimated DMI was significantly reduced by 6.45% and 3.26% in dairy and beef cattle, respectively, with increases in CHBr 3 dose resulting in larger DMI reductions. The significant reduction in DMI did translate into a significant effect on milk yield (−4.60%) at average CHBr 3 dose. Carrier type (oil vs. biomass), measurement technique, and cattle type influenced the results. The use of an oil carrier was associated with more pronounced reductions, particularly in CH 4 intensity. Additionally, respiration chambers yielded significantly greater CH 4 reductions compared with other measurement methods. This study highlights the CH 4 -mitigating potential of feed ingredients containing CHBr 3 , providing predictive models to optimize CH 4 reduction strategies under diverse production conditions. Future research should address long-term effects, dietary optimization, and practical implementation.