Opportunities of Asparagopsis sp. cultivation to reduce methanogenesis in ruminants: A critical review

Ruminant farming represents the largest anthropogenic source of methane, a greenhouse gas with similar to 30 times the global warming potential of carbon dioxide. To reduce enteric methane production in ruminants, macroalgae, such as Asparagopsis (Rhodophyta), have been trialed as feed additives. In vivo trials have reported up to a 98 % reduction in methane from cattle, when Asparagopsis taxiformis is included in their feed at 0.2 % organic matter. These observations have been widely attributed to the high bromoform content of Asparagopsis. However, inclusion of Asparagopsis has also been shown to adversely impact production of volatile fatty acids and feed intake. There are inconsistent results reported in the literature surrounding the effects of bromoform-containing seaweeds on ruminants, with the cause of rumen modification from in vivo trials not fully elucidated. On top of this, there are current difficulties surrounding the cultivation and distribution of Asparagopsis, both presenting barriers to its implementation on large scales. Further, detailed studies are required to implement this technology in a manner that is safe and effective for both animals and humans. This review aims to provide an overview of the current scientific standings of this technology and summarises the areas which require further investigation.