Feeding a higher-starch diet reduced enteric methane emissions in lactating dairy cows by 14%, but it did not change which animals consistently produced the most methane, according to preliminary research presented during a recent University of Wisconsin-Madison Badger Dairy Insight webinar.
In a crossover study involving 64 Holstein cows, researchers found animals largely maintained their ranking as either high or low methane emitters after switching between diets containing 20% or 30% starch. Because each cow received both diets during the trial, researchers were able to evaluate whether changes in nutrition altered an individual animal’s methane production. The findings suggest nutritional strategies can lower enteric methane emissions across a herd, but individual animal biology may ultimately influence how much methane a cow produces.
“The higher emitters tend to stay high regardless of the diet and the lower emitters tend to stay low,” says Daniel Vieira, Ph.D. student in the University of Wisconsin-Madison Department of Animal and Dairy Science.
Higher Starch Improved Efficiency and Reduced Methane
Researchers evaluated cows over two five-week feeding periods. Compared with the reduced-starch diet, the higher-starch ration decreased dry matter intake by 1.5 kg/day, increased milk production by 0.8 kg/day, improved feed efficiency by nearly 6% and reduced methane emissions by 14%. Methane yield, methane produced per kg of feed intake, and methane intensity, methane per kilogram of milk produced, also declined.
Geda explained that increasing dietary starch changes rumen fermentation, shifting production toward propionate rather than acetate. That shift helps explain why methane production fell despite maintaining milk production. Propionate formation consumes hydrogen, leaving less available for methanogenic archaea to convert into methane. The findings suggest dietary starch can improve feed efficiency while simultaneously reducing methane emissions, highlighting the close relationship between rumen fermentation and methane production.
“Propionate uses hydrogen. Meanwhile, acetate production releases hydrogen into the rumen. Less hydrogen means less methanogenesis,” Vieira explains.
The results add to growing evidence that methane mitigation is closely tied to improving rumen efficiency rather than simply suppressing methane-producing microbes.
“Methane is not only a greenhouse gas, it’s also an energy loss from our diets,” Vieira says. “The idea is reducing methane emissions by using that carbon to produce more milk protein and use it in a productive way.”
Methane Rankings Remained Consistent
The consistency of methane-emission rankings across both diets was one of the study’s most notable findings. If diet were the primary driver of methane production, researchers would expect cows to move up or down in the rankings after switching rations. Instead, animals that ranked among the highest methane producers on one diet generally remained among the highest producers on the other, while lower-emitting cows continued to produce comparatively less methane.
Strong correlations were observed for methane production, methane yield and methane intensity between feeding periods, suggesting that individual animal characteristics, including genetics or the rumen microbiome, may play a significant role in methane production beyond diet alone.
Researchers Shift Focus to Hydrogen Metabolism
Those observations align with a broader shift in methane research described by Dr. Hilario Mantovani, associate professor of animal and dairy science at the University of Wisconsin-Madison.
Mantovani explained that methanogenic archaea typically account for less than 5% of the rumen microbial community, yet they play an essential role in rumen function by removing hydrogen generated during fermentation. Without a pathway to use that hydrogen, fermentation becomes less efficient. While directly inhibiting methanogens has become increasingly feasible through feed additives such as 3-NOP and other compounds, researchers are now focusing on what happens to that hydrogen once methane production is reduced.
“The challenge is to redirect this pool of hydrogen to other end products that can actually be used by the animal,” Mantovani says.
Redirecting hydrogen into products such as propionate or microbial protein could improve feed efficiency while simultaneously reducing methane losses. Mantovani said that goal is becoming increasingly important as researchers evaluate new methane inhibitors and combinations of feed additives.
“Reducing methane isn’t the main issue. Redirecting the hydrogen is the key to effective mitigation,” he says.
While nutritional strategies such as increasing dietary starch continue to demonstrate measurable reductions in methane emissions, the Wisconsin findings suggest they may be only one piece of the puzzle. Future mitigation efforts could combine diet, targeted feed additives and, eventually, selection of cattle that are naturally lower methane emitters, offering multiple tools to improve both efficiency and environmental performance.
