DENVER — Cows should be outside.

That’s the position of a Colorado-based grocery store chain that recently announced it will carry only dairy products from farms where cows graze in pastures.

Natural Grocers by Vitamin Cottage claims grazing improves the health of cows, consumers and the environment, and it hopes to expand an ongoing, national debate over how to best care for livestock.

The American Grassfed Association, which helped Natural Grocers develop its rules, said it is the first retail chain to carry only pastured dairy products; many already have rules barring suppliers from such things as keeping chickens and pregnant pigs in cramped cages.

But the issue isn’t as straightforward as it might seem as weather prevents most farms in the United States from grazing year-round. With no clear guidelines on what qualifies as “pasture-raised,” consumers paying a premium for grass-fed milk might be confused about what they are buying.

Natural Grocers was one of the first retailers in the 1990s to ban dairy products from farms that used growth hormones or excessive antibiotics, said Heather Isely, whose parents founded the business in 1955. Over time, the family decided that wasn’t enough.

“Consumers are buffeted with all these image of cows grazing on pasture when it comes to dairy,” Isely said. “When you talk to most people, that’s what comes to mind ... and we wanted to become completely transparent and lift that veil away and say, you know, that’s not always the case and you really do need to take a more careful look at your dairy products.”