Vitamin B12 is unlikely to explain why seaweed-based feed cuts cow methane less on high-fiber diets. According to Gram Research analysis of 2026 lab experiments, B12 at natural rumen levels did not weaken bromoform’s methane-blocking effect, and only very high amounts, such as 422 mg/L, reversed it.
Seaweed from the Asparagopsis group and a chemical called bromoform can cut methane burps from cows, but they work less well when cows eat high-fiber diets. Scientists wondered if vitamin B12, which gut microbes make more of on high-fiber diets, could be the reason. According to research reviewed by Gram, lab experiments on cow stomach microbes found that vitamin B12 at normal levels did not weaken bromoform’s methane-blocking effect. Only very large amounts of added B12 reversed it, far more than the rumen naturally contains. The researchers concluded that vitamin B12 is unlikely to explain the weaker results seen in live animals. They noted that real-world measurements of how bromoform moves through the rumen are still needed to rule this out completely. The study was published in 2026 in the journal Animal.
Key Statistics
A 2026 lab study published in the journal Animal found that vitamin B12 at normal rumen levels did not weaken bromoform’s ability to block methane in cow stomach microbe cultures.
In a 2026 in vitro experiment, the team reported that only a spike of 422 mg/L of vitamin B12 markedly reversed the methane-reducing effect of bromoform at 0.50 µM.
A 2026 study of dried Asparagopsis seaweed found that vitamin B12 at physiological concentrations did not affect its ability to inhibit methane production in lab cultures.
The Quick Take
- What they studied: Researchers asked whether vitamin B12 might explain why seaweed and bromoform, a compound found in it, reduce cow methane less well when cows eat high-fiber feed.
- Who participated: No animals took part. The team used samples of mixed stomach microbes from cows, grown in lab dishes and tubes. The study ran one long series of transfers and three shorter batch experiments, and the sample count was not reported.
- Key finding: Vitamin B12 at normal rumen levels did not weaken bromoform’s ability to block methane. Only very high added amounts, such as 422 mg/L, reversed the effect, which is much more than the rumen naturally holds.
- What it means for you: Vitamin B12 is probably not the reason seaweed feed works less well on high-fiber diets. This is lab evidence only, so it does not yet prove how the feed works inside a living cow, and it should not change how farms or pet owners feed animals.
The Research Details
Cows have a large first stomach called the rumen, where billions of microbes break down plants. Some of these microbes make methane, a gas that is released when cows burp. Earlier work showed that seaweed from the Asparagopsis group, and bromoform, a chemical it contains, can block the step that makes methane. Yet these products tend to work less well when cows eat high-fiber diets, and no one knew why.
The researchers focused on a possible explanation. High-fiber diets encourage microbes to make more vitamin B12, and bromoform may react with B12 instead of with the methane-making step. If that were true, extra B12 should weaken bromoform’s effect. To test this, the team grew rumen microbes in lab cultures. In one long experiment, they moved the cultures through five rounds of transfers. Three other experiments used single batches, and each tested different amounts of B12, bromoform, or dried seaweed.
The team measured how much methane the cultures made and checked which types of methane-making microbes were present. They compared cultures with and without added B12 to see whether the vitamin changed the results. Because the experiments were run in a lab rather than in animals, the researchers could control each ingredient closely.
Lab cultures let scientists test one possible cause at a time. If vitamin B12 had a strong effect, it would have shown up clearly in these controlled dishes. Testing several amounts, including amounts close to what the rumen naturally contains, also shows whether the effect would matter in real cows. Repeating the tests with different setups makes the finding more believable.
The study used several linked experiments, which strengthens confidence in the pattern. The researchers tested both realistic and very high vitamin B12 levels, so readers can see where the effect starts. However, the sample size was not reported, and the work used lab cultures rather than live animals. Lab results can differ from what happens in a cow’s stomach, where feed, saliva, and microbe communities are more varied. The journal’s impact factor was not provided, so it is not included here.
What the Results Show
In the first and longest experiment, the team added vitamin B12 to lab cultures in small amounts over several transfers, and also in one larger spike. The small amount was 8.86 mg/L, and the spike was 422 mg/L. Only the very high spike clearly reversed the methane-reducing effect of bromoform at 0.50 µM. The same experiment also showed a rise in a group of methane-making microbes called Methanobrevibacter, which fits with bromoform’s usual action.
In two other experiments, B12 at much higher maximum levels of 500 mg/L and 10.0 mg/L did not weaken bromoform’s effect at 5.0 µM and 0.50 µM. This means that even when B12 was present in amounts that could be considered high, bromoform still blocked methane. The pattern held across the different bromoform doses that were tested.
In the fourth experiment, B12 at levels typical of the rumen did not change how well dried Asparagopsis seaweed blocked methane. This matters because seaweed is the product farmers actually use, not just pure bromoform. The researchers also noted that the amounts needed to reverse bromoform’s effect were far above what is found naturally in the rumen. Together, these results point away from B12 as the cause of the weaker effect on high-fiber diets.
The team reported that the change in methane-making microbes followed the same pattern as the change in methane. When B12 reversed the effect, the Methanobrevibacter group increased again, showing that the cultures were responding in a consistent way. This adds some confidence that the measurements reflected real biological changes rather than random noise.
Earlier work had shown that bromoform and related compounds block methane by reacting with a B12-related molecule that helps move a methyl group in the methane-making process. This study builds on that idea by asking whether natural B12 in the rumen could soak up bromoform before it reaches its target. The results suggest that, at natural levels, B12 is not a major obstacle, which narrows the list of possible explanations for why high-fiber diets reduce seaweed’s effectiveness.
The biggest limit is that these were lab experiments. Cows have a complex stomach environment, and bromoform may move, break down, or get absorbed in ways that lab cultures cannot copy. The authors themselves say that real measurements of bromoform, dibromomethane, and bromomethane inside living animals are still needed. The sample size was not reported, and the number of repeated runs for each condition was not clearly stated in the summary, which makes it harder to judge how steady the results are. Finally, the study tested only some combinations of diet and feed products, so other factors may still play a role.
The Bottom Line
Confidence is moderate that vitamin B12 is not the main reason seaweed works less well on high-fiber diets. This conclusion comes from several lab experiments that agreed with one another. It should not be treated as final, because no live-animal data were included. Farmers and feed companies should keep using current guidance and watch for new studies that measure what happens inside cows directly.
Livestock researchers, farm advisors, and feed makers who work on lowering cow methane will find this useful, because it rules out one possible explanation. Cattle and dairy producers may be interested, but they should wait for animal studies before changing feed plans. Everyday readers who do not work with cattle or livestock feed do not need to act on this finding.
Changes in feed practices take time, usually months to years, because they require animal trials, safety checks, and approvals. This lab finding is an early step. Any practical change would depend on future studies in living cows, which may take several years to complete.
Frequently Asked Questions
Does vitamin B12 make seaweed feed less effective for cows?
Lab research published in 2026 suggests it does not. Vitamin B12 at normal rumen levels did not weaken bromoform’s methane-blocking effect in cultures, and only very high added amounts reversed it. Researchers say live-animal studies are still needed to confirm this.
Why does seaweed reduce cow methane less on high-fiber diets?
The cause is still unclear. Researchers tested vitamin B12, which increases on high-fiber diets, as a possible explanation. The 2026 lab results suggest B12 is unlikely to be the reason, so other factors are being investigated.
What is bromoform and how does it reduce cow methane?
Bromoform is a chemical found in certain red seaweeds. It blocks the final steps of methane production in the cow’s rumen, the large first stomach. Research shows it can strongly reduce methane in lab cultures, though its effect in live cows varies with diet.
Has this study tested seaweed feed in live cows?
No, this 2026 study used lab cultures of rumen microbes, not live animals. Researchers said real measurements of bromoform inside living animals are still needed to fully rule out vitamin B12 as an explanation for weaker results.
Want to Apply This Research?
- If you use the app to follow sustainability or farm-related topics, log the type of feed or supplement you read about and the date you first learned about it. Then track any related updates from trusted sources, such as university extension offices or peer-reviewed journals.
- Use the app to set a reminder to check for new research on livestock methane every three months. When you find a new study, compare its sample size, study type, and whether it used live animals before deciding how much weight to give it.
- Over the long term, keep a simple log of research updates on methane-reducing feed additives, noting whether later studies test cows directly and whether they confirm or challenge the lab findings. This record helps you see how the evidence builds over time.
This article summarizes a laboratory study using cultures of cow stomach microbes, not live animals or people. Results may not apply to real farm animals, and this information is for general education only. It is not advice on feed, livestock management, or health. Consult a qualified animal nutritionist or veterinarian before making changes to animal diets.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.