Methane is a large source of greenhouse gas emissions in the United States.
Beef and dairy cattle produce over a quarter of the United States’ methane emissions.
Seaweed can reduce methane emissions when introduced as an additive in cattle diets.
Current global seaweed production is not sufficient for mass adoption in U.S. cattle diets.
Greenhouse gases trap heat in the atmosphere. Methane accounts for 11% of U.S. greenhouse gas emissions and are emitted from livestock for agriculture, the production and distribution of natural gas and crude oil, and coal mining (EPA 1, 2022). Around 58% of global methane emissions come from humans (EPA 1, 2022).
The agriculture sector is the largest source of methane emissions in the United States (EPA 1, 2022). When livestock such as cows, pigs, and sheep digest food, they produce and emit methane. This process is estimated to produce around 27% of the United States' methane emissions (EPA 1, 2022).
Preliminary experiments have introduced seaweed for up to 1% of dairy and beef cattle diets. In these tests, different types of red seaweed resulted in the largest methane emissions reductions. This may be due a compound in the seaweed called bromoform that reduces gut microorganisms that emit methane (Vijn, 2020).
The difference in the reduction in methane emissions between beef and dairy cattle could be due to the different types of seaweed used or the different breeds of cattle used.
Beef and dairy cattle fed with seaweed required less feed in order to gain weight (Lean, 2021). In some cases, dairy cows fed diets with seaweed produce more milk than cows without seaweed (Roque, 2019; Sefenoni, 2021).
Bromoform is suspected to cause cancer, and the Environmental Protection Agency (EPA) has set a limit of 0.08 mg/L for bromoform in drinking water (EPA, 2018; EPA, n.d.).
Beef and milk from cows fed seaweed have elevated levels of iodine (Stefenoni, 2021). While beneficial for those with insufficient iodine, excess iodine intake can lead to thyroid problems (Vijn, 2020; IM, 2001). The National Academies of Science has defined upper limits for safe iodine consumption based on age and other factors such as pregnancy (IM, 2001).
In 2018, 32 million tonnes of seaweed was produced globally, tripling since 2000 (Figure 1) (FAO, 2020). Over 95% of the production is in China, Indonesia, South Korea, and the Philippines (FAO, 2020).
Financial incentives may be necessary for seaweed adoption if increased beef or milk yields do not outweigh feed costs (Vijn, 2020). Improved feed efficiency could decrease the amount of feed necessary to raise cattle and reduce feed costs, which often comprise a large portion of costs on a farm (Roque, 2021). However, currently there are no scientific studies that have comprehensively investigated the economic costs for farmers to implement seaweed in cattle feed.
These seaweeds are not required to undergo premarket review and approval by the FDA. More research may be needed to classify the types of seaweed that reduce methane emissions as generally safe according to FDA regulations (Vjin, 2020).
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