MINNEAPOLIS – As pork producers build new barns and retrofit old ones to give hogs more space, they say consumers opposed to keeping pregnant sows in tight cages can expect to pay for their clearer consciences with higher food prices.

Under pressure from animal rights activists and sensing a shift in consumer sentiment, several major pork producers have agreed to phase out gestation crates and switch to more open pens. Major pork buyer McDonald’s Corp. recently announced its suppliers will have to stop using them.

“The McDonald’s announcement was a tipping point in the debate about gestation stalls versus pens. … That announcement has fundamentally changed the way people are looking at this debate,” said Dennis Treacy, executive vice president and chief sustainability officer for Smithfield Foods Inc., the world’s largest pork producer.

But the move to group pens requires building new barns and renovating old ones, more labor and more training for workers. Veterinary costs can go up because sows tend to fight and sometimes injure each other. Experts say at least some of those expenses are likely to be passed on in the price of ham, bacon, chops and sausage.

Smithfield had converted 30 percent of its company-owned farms by the end of December and is on track to meet its goal of switching all of them by 2017, Treacy said.

Some pork producers are proud they’ve never used gestation crates. They include Paul Willis, who founded the pork operations of Niman Ranch Inc., which supplies restaurants and supermarkets with humanely raised pork

Willis, who farms in Thornton, Iowa, said customers are willing to pay premium prices for the pork he and more than 500 other farmers raise according to Niman’s standards.

“We think our system may be the best and most efficient in the long run for the animals, for the people, for the farmers and the environment,” he said.