The world’s ruminant livestock —cows, sheep, and goats— are responsible for approximately 30% of global anthropogenic methane emissions, a greenhouse gas that traps heat 25 times more efficiently than CO₂.
This methane is mainly released through burps, respiration, and ruminal flatulence, and accounts for 17% of global food system emissions.
A silent climate bomb: ruminal methane and its global impact
Methane generated by ruminant livestock equals 5% of total greenhouse gas emissions (GHG) worldwide.
Its release is directly related to digestive fermentation in the gastrointestinal system of these animals, and its volume increases in parallel with global consumption of livestock products.
Algae diets: a food innovation to mitigate emissions
In 2025, a research team led by the Estación Experimental del Zaidín (CSIC, Granada), along with Queen’s University (United Kingdom) and Teagasc Centre (Ireland), demonstrated that incorporating seaweed into ruminant diets can reduce methane emissions by up to 40% in laboratory conditions.
The species analyzed include:
- Himanthalia elongata
- Fucus vesiculosus
- Alaria esculenta
- Ascophyllum nodosum
- Asparagopsis taxiformis
- Chondrus crispus
These algae were selected for their biomass availability, biochemical composition, and geographical origin, and stand out for their high content of phlorotannins, antioxidant compounds with a methane inhibiting effect.
Algae an alternative against livestock emissions
In vitro trials: measuring digestion and gas emissions
An incubation system simulates ruminal fermentation to assess the impact of algae.
The Zaidín team designed an experimental protocol that involves:
- Incubating ruminal fluid with algae-enriched diets
- Simulating fermentation with carbon dioxide in glass bottles
- Maintaining the mixture at 39°C in incubators
- Measuring gas production and analyzing methane concentration through chromatography
This method allows evaluating multiple samples in a short time, facilitating comparison between species and algae extracts.
Dose adjustment and microbial adaptation: challenges for practical application
“If we exceed 1% inclusion in the diet, it can affect digestion and reduce consumption,” warns David R. Yáñez-Ruiz, the study’s lead researcher.
Furthermore, prolonged trials show that rumen microorganisms can adapt and degrade anti-methane compounds, which could reduce effectiveness of algae over time.
Next steps: in vivo studies and long-term fermenters
The team plans to move towards in vivo trials with ruminants, using long-duration fermenters to observe:
- Adaptation of ruminal microbiota
- Effects on animal health and productivity
- Real environmental impact on livestock systems
Beyond algae: garlic and other agri-food residues under study
The inclusion of byproducts like garlic also shows potential for reducing emissions.
In addition to algae, garlic waste is being evaluated in the diet of Merino lambs, with positive preliminary results in reducing greenhouse gas emissions.
