The role of seaweed as a potential dietary supplementation for enteric methane mitigation in ruminants: Challenges and opportunities

Abstract

Seaweeds are macroalgae, which can be of many different morphologies, sizes, colors, and chemical profiles. They include brown, red, and green seaweeds. Brown seaweeds have been more investigated and exploited in comparison to other seaweed types for their use in animal feeding studies due to their large sizes and ease of harvesting. Recent in vitro and in vivo studies suggest that plant secondary compound-containing seaweeds (e.g., halogenated compounds, phlorotannins, etc.) have the potential to mitigate enteric methane (CH₄) emissions from ruminants when added to the diets of beef and dairy cattle. Red seaweeds including Asparagopsis spp. are rich in crude protein and halogenated compounds compared to brown and green seaweeds. When halogenated-containing red seaweeds are used as the active ingredient in ruminant diets, bromoform concentration can be used as an indicator of anti-methanogenic properties. Phlorotannin-containing brown seaweed has also the potential to decrease CH₄ production. However, numerous studies examined the possible anti-methanogenic effects of marine seaweeds with inconsistent results. This work reviews existing data associated with seaweeds and in vitro and in vivo rumen fermentation, animal performance, and enteric CH₄ emissions in ruminants. Increased understanding of the seaweed supplementation related to rumen fermentation and its effect on animal performance and CH₄ emissions in ruminants may lead to novel strategies aimed at reducing greenhouse gas emissions while improving animal productivity.

Keywords: Bromoform; Cattle; Methane; Phlorotannins; Ruminant; Seaweed.

Fig. 1

Various seaweed species (0.2 g OM/seaweed species; green-, brown-, and red-seaweed) and in vitro methane (CH₄) production (mL/g OM) (Adapted from Machado et al., 2014). Con = Control (1 g of Flinders grass + 0.2 g of decorticated cottonseed meal as a positive control, OM basis). Samples of 1 g of Flinders grass + 0.2 g of all other seaweed (OM basis) were used in this study). C. coelothrix = Cladophora coelothrix; C. patentiramea = Cladophora patentiramea; U. ohnoi = Ulva ohnoi. Pooled rumen fluid as an in vitro inoculum was collected from three fistulated steers (Bos indicus) fed Flinders grass (Iseilema membranacea) hay. A arrow indicates a lower CH₄ production from seaweed species.

Fig. 2

In vitro correlation between the concentration of halogenated compounds (bromoform or bromochloromethane (BCM; mg/g OM) and the methane (CH₄) emissions (mL/g OM) in the Asparagopsis taxiformis (cut off: < 1.0% of bromoform or BCM (mg/g OM). Adapted from Goel et al. (2009) and Vucko et al. (2017). OM = organic matter.

Fig. 3

Proposed schematic microbial fermentation of plant secondary compound (e.g., bromoform, BCM)-rich seaweed and methane (CH₄) reduction pathways in the rumen. Three major pathways of methanogenesis are known: hydrogenotrophic, methylotrophic, and acetoclastic pathways. A/P ratio = acetate-to-propionate ratio; BCM = bromochloromethane, MCR = methyl CoM reductase; VFA = volatile fatty acids; GHG = global greenhouse gas. Sources: Wood et al. (1968), Bapteste et al. (2005), Denman et al., 2007a, Denman et al., 2007b, Attwood and McSweeney (2008), Frey (2010), Allen et al. (2014), Patra (2012, , Machado et al. (2016), Danielsson et al. (2017), Machado et al. (2018), and Roque et al. (2020).