Every glass of milk carries an invisible climate cost. Cows burp methane in massive quantities as they digest their feed. Scientists have long searched for ways to shrink that footprint.
They usually target how much gas each individual animal produces.
A new study took a completely different approach. The team looked at a routine choice farmers already make every day. They focused on the type of concentrate pellet tossed in the feed bin alongside pasture grass.
Could this change how much methane hides in every single gallon of milk?
Why farmers have always had to fill a summer gap
To find out, they gathered 72 late-lactation cows for a 36-day trial. They used two trailer-mounted breath-sampling units to track the results on pasture.
Perennial ryegrass is the workhorse of pasture-based dairy farming. It grows densely in spring and autumn, but summer heat thins it out. This happens right when late-lactation cows need it most.
These animals face a demanding double burden. They are still producing milk while carrying their next calf.
Energy needs are high, and the pasture can no longer keep up.
Farmers have long solved this with concentrate pellets handed out at milking time.
This standard practice bridges the seasonal nutritional gap. It is inexpensive and used across grass-fed dairy regions worldwide.
Nobody had tested whether the type of carbohydrate in those pellets made a difference to emissions.
The two options are starch or fiber. They had each been studied separately in barns or against unrelated diets. They were never tested head-to-head on pasture under real grazing conditions.
How the trial was designed and measured
The research team was led by Maria M. Della Rosa of the Bioeconomy Science Institute. They worked with a herd at Massey University’s dairy farm in Palmerston North.
They divided 72 late-lactation cows into four groups. One group grazed on pasture alone without any supplements.
The other three received roughly 11 pounds of concentrate pellets per day at milking time. These pellets were either high-starch, high-fiber, or an even mix of both.
Measuring what a grazing cow breathes out isn’t straightforward.
Two trailer-mounted units lured cows in with feed and sampled breath over 36 days.
Not every cow visited often enough to generate reliable data. Therefore, the final analysis drew on 60 animals.
Collars tracked how long each cow spent eating and chewing cud. Milk was weighed at every milking and tested for fat and protein content.
These two measures determine a milk’s nutritional value. In this study, they also determined the climate math.
The result that surprised the researchers
The prediction going in seemed reasonable to the team.
Starchy feed packs more energy, while fibrous feed adds bulk. Each type was expected to nudge daily methane output in a different direction.
The breath data said otherwise.
Across all four diets, the cows produced nearly identical amounts of methane each day. Replacing starch with fiber, or skipping pellets entirely, barely moved the needle on total emissions.
Milk production told a very different story.
Cows on high-starch and mixed diets gave about 16% more fat-and-protein-corrected milk than the grass-only group.
Fiber-fed cows landed somewhere in between. Fat and protein concentrations held steady across all four groups.
This wasn’t richer milk, just more of it.
Dilution, not elimination: The climate math behind the finding
Each cow’s methane output stayed flat while milk production rose. Consequently, the gas footprint per unit of milk fell by roughly 13% to 14% for the starch and mixed groups.
This occurred without any additives or new technology.
It simply means more milk spreading the same methane across more grocery store gallons.
The underlying mechanism is simple dilution.
Each cow still burps the same amount of gas. But when that gas is divided across more milk, the per-glass footprint shrinks. It is basic arithmetic, not chemistry.
A secondary pattern emerged from the collar data.
Cows that spent more time chewing per pound of feed showed a higher methane footprint per unit of milk. This wasn’t because they emitted more gas. Instead, they produced less milk, pushing their per-unit figure upward.
The relationship was moderate, and grass intake was difficult to untangle.
One modest finding stood out on the fiber side.
High-fiber cows released less methane per pound of feed consumed than the grass-only group.
What this means for farms — and what it doesn’t
The practical appeal here is absolute simplicity.
Farmers already use summer pellets to maintain production. Shifting toward starch-leaning formulas requires no new equipment, no additives, and no routine changes. The infrastructure is already in place.
The limits of the study matter, though.
Researchers couldn’t precisely measure how much pasture grass each cow consumed. That variable could influence results.
Because individual emissions didn’t fall, a farm’s total footprint only decreases if the same milk output comes from fewer animals overall.
In grass-fed dairy regions, which account for a large share of global production, a 13% to 14% reduction in emissions intensity could scale meaningfully.
Replicating these results across different seasons, breeds, and farm systems is the logical next step. The study, published in Frontiers in Veterinary Science, opens an unexpected door.
It turns out that the most effective tool to slice dairy emissions isn’t a complex lab chemical or an expensive high-tech gadget; it is the humble starch pellet already sitting inside the American feed bucket.
Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.
