Gut bacteria could be key to producing tastier cow’s milk

It's not just good breeding and tasty grass that make a dairy cow a champion milk producer. It's also the microbes that live in the animal’s gut. Now, researchers say they know which microbes lead to the best milk.

The finding suggests new ways to improve milk and reduce methane emissions from cows—a major source of the greenhouse gas—says Diego Morgavi, an animal scientist at the French National Institute for Agricultural Research in Clermont-Ferrand-Theix who was not involved with the work.

Cows and other ruminants such as goats and sheep have a special stomach called a rumen that houses millions of microbes. These organisms break down hay, grass, and other hard-to-digest plant material into usable nutrients and calories. A downside is that ruminants burp and fart out 100 million tons of microbe-generated methane a year worldwide, making them the second-biggest human-related contributor of this greenhouse gas, after rice cultivation.

To see how these microbes play a role in milk quality and methane production, Itzik Mizrahi, a biologist at Ben-Gurion University of the Negev in Beersheba, Israel, teamed up with John Wallace, an animal scientist at the University of Aberdeen in the United Kingdom, to characterize the microbes in several herds of cows and to see whether those microbes influence any of hundreds of traits, such as growth rate, milk quality and quantity, and methane production.

They collected microbial DNA and information about those traits from more than 1000 cows on seven farms in the United Kingdom, Italy, Sweden, and Finland. The cows were Holsteins and Norwegian Reds—two breeds that constitute the majority of dairy livestock in Europe.

From the DNA, the team identified the microbes in each cow’s gut and compared communities to see what bacteria, protozoa, fungi, and other microbes they had in common. Then the researchers used machine learning—sophisticated computer programs that can find connections among massive amounts of disparate data—to figure out how microbes might influence particular traits.

Although each cow had a unique microbiome, half of the animals had 512 microbial species in common, the team reports today in Science Advances. The analyses indicated that 39 “core microbes” are more powerful than genes in determining how tasty a cow’s milk is, and even how much methane it produces.

Gut microbes have a surprisingly powerful effect on these traits, says Fabio Lima, who studies the cow microbiome and milk production at the University of Illinois in Urbana. Morgavi would like to see whether other cow breeds have the same core microbes. But in the meantime, he thinks that giving certain microbes to calves in their food—similar to probiotics people take—might reduce methane production.

Manipulating an entire population of microbes will be challenging, notes Lima, who is already trying to do just that to improve milk taste or quantity. But at least it’s now clear that adding certain microbes to the gut can make a difference, Wallace says.