Milk’s carbon footprint can change dramatically for a surprising reason
A five-year dairy study reveals how producing more milk can shrink its carbon footprint – and why the way emissions are counted matters.
Milk is part of everyday life for millions of people, but producing it also creates greenhouse gases.
That makes dairy part of a much bigger question about food: how can farms produce enough nutrition without creating more climate pollution than necessary?
Carbon-footprint numbers are often used to compare foods, farms, and even countries.
But a new analysis from Bangladesh shows that those numbers can change a lot depending on how much milk cows produce and, just as importantly, how emissions are counted.
Why milk emissions matter
Cattle release methane as they digest food, while manure, growing animal feed, fuel, and electricity create additional emissions.
When all of these sources are added together, they form part of milk’s carbon footprint.
That number can influence how people think about the environmental cost of food. It may also shape decisions about farming practices, climate targets, and how food from different countries is compared.
The work was led by Dr. Elias Uddin, an assistant professor of animal science at the University of Connecticut.
The team analyzed five years of information from the Bangladesh Agricultural University Dairy Farm.
“You have to account for those non-lactating animals, because those are part of the production system,” Dr. Uddin said. “You cannot just avoid them because they don’t produce milk.”
The whole herd counts
That point matters because a dairy farm includes many animals that are not producing milk at a given moment. Dry cows, young animals, and heifers still eat feed, produce manure, and release methane.
In fact, lactating cows were responsible for about 40% of the farm’s greenhouse-gas emissions. The remaining 60% came from animals that were not producing milk.
The researchers counted emissions from cattle digestion, feed production, manure, and farm energy use.
They followed the system up to the point where milk and live animals left the farm, but they did not include processing or transportation after that point.
Across the five years, digestion was the largest contributed 20%, and farm energy use made up the remaining 8%
More milk changed things
One of the biggest changes during the five-year period was how much milk each cow produced. Average daily milk yield rose by about 63%, from 7.8 pounds (3.53 kilograms) per cow to 12.7 pounds (5.76 kilograms).
At the same time, greenhouse-gas emissions per unit of milk fell.
Under one of the main calculations, the footprint dropped by about 37%, from 6.89 to 4.34 kilograms of carbon dioxide equivalent per kilogram of fat- and protein-corrected milk.
That term simply means the milk amount was adjusted for differences in fat and protein. It gives researchers a more consistent way to compare milk production from year to year.
“We saw that increasing productivity is really a crucial thing, and very important to reduce the carbon footprint,” Dr. Uddin said.
“In developing countries, increasing efficiency and productivity is key to reducing carbon footprint rather than hitting only emissions mitigation strategies.”
Better output, same emissions
The reason is fairly simple. If a farm produces more milk while total emissions stay similar, those emissions are spread across a larger amount of food.
That does not mean the farm’s total greenhouse-gas pollution dropped by 37%.
The researchers found that total farm emissions remained fairly stable, so most of the improvement came from producing more milk for roughly the same overall emissions.
The higher milk production happened alongside changes in feeding and herd makeup.
The farm used more high-yielding Holstein Friesian crossbred cows, while the quality and energy content of the diet also improved.
Because several changes happened together, the analysis cannot show exactly how much each change contributed on its own.
Accounting changes the milk footprint
The most surprising part of the work may be how much the final carbon-footprint number depended on the accounting method.
Bangladeshi cattle farms often raise animals for both milk and meat. That makes them different from systems where milk production and beef production are more clearly separated.
If the researchers assigned all farm emissions to milk, the five-year average footprint was 5.18 kilograms of carbon dioxide equivalent per kilogram of corrected milk.
When they divided emissions between milk and meat based on how the animals used energy for each product, the milk footprint fell to 2.74 kilograms.
“If we use that traditional allocation method of emission, it overestimates emissions,” Dr. Uddin said.
“But if we use the specific allocation method that is applicable for production system in Bangladesh, it really gives you a different answer.”
Local data changed estimates
The team also compared two methods used by the Intergovernmental Panel on Climate Change (IPCC) to estimate livestock emissions.
One method, called Tier 1, estimates emissions using broad, standard values. Tier 2 uses information from the farm itself, such as what the cows eat, how much milk they produce, their body size, and how manure is handled.
For this farm, Tier 1 estimated about 7.11 kilograms of carbon dioxide equivalent per kilogram of milk, while Tier 2 estimated about 5.18 kilograms per kilogram, which was 27% lower.
The farm did not suddenly emit less greenhouse gas. The difference came from using a calculation that better matched how this particular farm actually operated.
“We can see which farms are doing better compared to others, and the farm that has a low footprint, the practices they’re doing, can those be translated into key messages that can be used by other farmers to make changes?” Uddin said.
Why people should care
For the public, the main lesson is that a carbon-footprint number is not as simple as it looks.
Two farms can produce similar foods but appear very different if they use different animals, different production systems, or different ways of allocating emissions between products.
That matters when food products are compared across countries. A number that ignores local farming systems could make one producer look worse even when the comparison is not being made on equal terms.
“Let’s say two different countries are exporting the same product at a similar price,” Uddin said.
“If one is more environmentally friendly than the other, importers are going to prefer the one that is environmentally friendly.”
Limitations of the study
The analysis followed only one institutional farm, so its numbers should not be treated as a national average for Bangladesh.
Small farms can differ greatly in feed, herd size, animal breeds, manure handling, and daily management.
Some emissions were also estimated using published values rather than measured directly on the farm.
The work did not include monthly or seasonal changes, and it did not track changes in soil carbon because suitable long-term measurements were unavailable.
Even with those limits, the five-year record shows why productivity and accounting choices matter when judging the climate impact of milk.
Producing more milk from the same overall system can lower emissions per unit of food, but fair comparisons still depend on counting those emissions in a way that matches how the farm actually operates.
The study is published in the Journal of Dairy Science.
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