Cows don’t look like climate troublemakers, but they play a bigger role than most people realize.
As cattle digest grass, they release methane – a gas that traps far more heat in the atmosphere than carbon dioxide in the short term.
Over time, that adds up. The International Energy Agency estimates methane has driven about 30% of global temperature rise since the industrial revolution.
Farmers and scientists have been trying to tackle this for years. It sounds simple. Change what cows eat to cut the gas they produce.
But things get tricky fast, especially on open grazing farms where animals roam across wide land and eat freely. You can’t control every bite. That’s where new ideas start to matter.
Seaweed enters the conversation
One idea has been quietly gaining ground: seaweed. Not the kind washed up on beaches, but a specific red variety called Asparagopsis. It contains a natural compound called bromoform, which can reduce methane production during digestion.
Now, researchers have tested whether this works outside tightly controlled feedlots. They looked at real grazing conditions, where cows live and feed as they normally would.
The team included PhD student Kellie Wenham and Dr. Mariana Caetano from the University of Adelaide’s School of Animal and Veterinary Sciences.
What the study found
The study followed 80 pregnant and lactating Angus cows over eight weeks. Some cows received a supplement made from bromoform extract oil. Others did not.
The results stood out. “Across the eight-week trial involving 80 Angus cows, methane emissions were reduced by between 49% and 77 % in cows receiving the supplement,” said Wenham.
“This is a substantial reduction, particularly in an extensive system where delivering consistent supplementation can be difficult.”
That level of reduction is hard to ignore, especially in grazing systems where consistency is usually the biggest hurdle.
What about the calves?
Any change in a breeding herd raises a basic question. What happens to the calves?
The researchers tracked this closely. Calves born to cows that received the supplement grew normally. Their weight gain from birth to 150 days stayed on track, with no signs of slowed development.
“This is critical. In breeding systems, it’s not just about the cow – you need to be confident there are no unintended consequences for their offspring,” said Dr Caetano.
That reassurance matters for farmers who depend on healthy calves for future herds and income.
Less feed, same performance
There was another detail that caught attention. The cows that received the supplement ate slightly less feed but maintained stable body weight.
That opens the door to possible savings. Feed is one of the biggest costs in cattle farming, especially when conditions are dry or pasture is limited.
“In a commercial setting, reduced feed intake without a drop in productivity could translate into meaningful savings,” noted Dr. Caetano.
“That’s an important incentive for adopting bromoform, alongside the environmental benefits.”
Lower emissions and lower costs rarely come together. When they do, people pay attention.
Not everything is settled yet
The study didn’t ignore the fine print. Some cows showed changes in blood chemistry, including mild metabolic alkalosis in a few cases. The shifts stayed within acceptable ranges, but they raised questions about long-term use.
“These changes were generally within acceptable ranges, but they highlight the need for further research into long-term health impacts and optimal dosing,” said Dr. Caetano.
Calves also showed minor changes in blood markers, though these stayed within normal limits. Nothing alarming, but enough to keep researchers cautious.
Reducing methane from grazing systems
Most earlier work on methane-reducing supplements has focused on feedlots, where animals eat measured diets. That’s easier to manage but represents only part of the cattle industry.
This study stands out because it tested the idea in grazing systems, where cattle roam freely and feeding is harder to control.
“Our findings show that bromoform-based supplements can be effective beyond feedlots, including in pasture-based systems that dominate Australian beef production,” said Dr. Caetano.
Study limitations and future research
The results point to a promising tool, but they don’t close the case.
Questions remain about how to deliver the supplement consistently in open fields, how much to use, and how animals respond over longer periods.
“There is real potential here, but adoption will depend on ensuring the approach is safe, practical and cost-effective for producers,” said Wenham.
“If we can get that balance right, this could be a powerful tool to help the livestock industry reduce its environmental footprint.”
That balance will decide whether seaweed-based solutions stay in research papers or become part of everyday farming.
The full study was published in the journal Frontiers in Animal Science.
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