The cows were silent on a recent July morning at Mill-King dairy farm in McGregor, Texas. They stood under shade trees, digesting their breakfast, while cicadas buzzed in the branches overhead.
"It's starting to warm up, so they're starting to get a little bit less ... frolicky," says Craig Miller, watching from the fence line.
His grandfather started this farm. Now he runs it, producing nonhomogenized milk from a mostly grass-fed herd. He says this cow behavior is exactly what he expects as the temperature rises.
"Any dairy farmer — commercial, small, local — are experts in dealing with heat," says Miller.
That is because the way cows digest food takes a lot of energy and generates a lot of heat. When it gets too warm outside, cows want to cool down. So they spend that energy panting, and as more blood flows to their skin, they sweat. They lose their appetite.
As Miller puts it: "They just stop eating. It's harder to get feed into them."
Without food, cows stop producing as much milk. The cows at Mill-King give about 33 percent less in the hot summer months. That means less money for this family business.
Even more troubling; Miller says he has noticed that summers are getting hotter. "Some people say it's global warming. I'm just doing what I can with what I've got," he says.
It is a problem dairy farmers in many parts of the country are confronting. One study finds the nation's dairy industry already loses $900 million a year to "heat stress." Another says global warming has already decreased U.S. milk production from Holstein cows by about 2 percent.
"There are a lot of cows that will be living in hotter climates," says Geoffrey Dahl, chair of the Department of Animal Sciences at the University of Florida, Gainesville.
Breeding a "slick cow"
Dahl says the problem is bigger than just hotter summers. His research shows how pregnant cows that suffer heat stress give birth to calves that also produce less milk. The phenomenon is similar to what people who study epigenetics see in humans.
"In utero, negative effects can lead to higher incidents of diseases later in life," says Dahl. "It's kind of a negative cascade that occurs."
He and his colleague are working on one solution. They have bred a new kind of dairy cow. It includes the DNA of a South American cow breed that has adapted to better withstand heat.
It's called a "slick cow," in reference to its fine coat of hair — which helps it handle higher temperatures.
Dahl says slick cows also seem to sweat more and transfer heat off their bodies more efficiently, so their milk production does not decline when it's warmer out.
The breed just entered the market six months ago.
"There are actually some bulls now that are available through a couple of the semen companies out there that have this slick gene," he says.
Fans and water
At the Southwest Regional Dairy Center in Stephenville, Texas, Barbara Jones is looking at more traditional ways of helping cows cope with the heat.
"We have fans here and we also have sprinklers," she says, walking through one of the barns, where cows munch on feed while water mists them from overhead.
"It should wet the cow to her skin," says Jones, "then those sprinklers will shut off. The fans will keep going, and we're going to employ that evaporative cooling to cool the cows."
The dairy center is on the campus of Tarleton State University, and Jones is researching how different cooling techniques affect milk production. She says these water and fan setups are pretty common in the South and Southwest, but they could be used more.
Dahl says they're also becoming more widely used in other parts of the country, like the Midwest and Northeast, as temperatures rise.
Back at Mill-King dairy farm, that doesn't surprise Miller. His farm also employs fans and sprinklers to cool his cows. But he points out that all of these solutions cost money.
"There's only so much you can do and be economically feasible," he says.
That could mean yet another consequence of a warming climate: more expensive milk.