Supplementing beef steer diets with Asparagopsis taxiformis seaweed reduced enteric methane production by up to 80%, with reductions persistent over the 21-week study period. The efficacy of the seaweed increased as the proportion of non-fiber carbohydrates in the diet increased. While DMI decreased in high seaweed groups, ADG was unaffected, leading to improved feed conversion efficiency. No bromoform residues were detected in the meat, but iodine levels increased with seaweed inclusion, albeit remaining far below toxicity limits for humans.

The study received funding from Elm Innovations, the David and Lucile Packard Foundation, and the Grantham Foundation. However, the authors state that the funding only covered experiment costs and that funders played no role in study design, data collection, analysis, publication decisions, or manuscript preparation.

This study demonstrates a significant reduction in enteric methane emissions from beef steers using a readily available natural feed additive (seaweed), potentially offering a sustainable solution for mitigating livestock's impact on climate change. The research is well-designed, uses appropriate methodology, and presents compelling results, but the small sample size, unclear economic implications, and increased iodine levels warrant further investigation and prevent a top rating of 5.