He credits most of the increase to breeding, more frequent milking, and better feed. Another factor comes straight from the biotech lab: biweekly injections of synthetic growth hormone.

If you don't like that, you won't like this:

As of Feb. 1 in Pennsylvania, consumers won't be able to tell the difference between milk from farms that inject their cows and milk from those that don't.

The state Agriculture Department has forbidden dairies that don't use the hormone from touting that fact on milk-bottle labels, contending it gives the impression that milk like Harnish's is unsafe.

It is the first such move in the nation, and the ensuing debate has spilled from the aisles at Whole Foods to the halls of Harrisburg, where the governor's office is reviewing the decision. The issue also has come up at hearings in New Jersey, though the state has proposed no change.

After extensive study, and 14 years after the U.S. Food and Drug Administration approved the hormone for use, there is indeed no proof that milk from injected cows is unsafe. But some researchers say questions about the drug's impacts remain unanswered.

And critics say its effects on bovine health - including an increase in mastitis, an udder infection - are reason enough to ban it. That's a key reason it cannot be used on cows in Europe and Canada.

At the very least, farmers should be allowed to say if they don't inject, said Michael Hansen, a senior scientist at the nonprofit Consumers Union. "Consumers have a basic right to know what's in the foods they eat, and how they are produced," Hansen said.

Yet Harnish, who farms 200 acres here in western Lancaster County, worries that some of his competitors' labels are misleading. A few have been downright inaccurate, making such claims as "hormone-free." All milk contains hormones, whether the natural or the almost-identical synthetic variety.

Harnish said his herd is just as healthy as it was before he started using the synthetic version, made by St. Louis-based Monsanto. He says the product, called Posilac, is one of the success stories of American technology.

"We're just born and bred to find the newest and the best and the fastest whatever way to do something," he said. "And so in the farming industry, we've done that."

Technically called recombinant bovine somatotropin (rBST), Posilac differs from natural bovine growth hormone by just one amino acid out of 191. At Harnish's farm, a cow gets a 500-milligram shot two months after she gives birth, then every 14 days thereafter.

Harnish said Posilac boosts his milk production by about 10 percent, though about half of the additional revenue is spent on the hormone and on extra feed needed to fuel the higher milk output.

Posilac is used on perhaps one-third of U.S. dairy herds, Monsanto officials said.

Milk from untreated cows is often a bit more expensive than that from treated animals. But it is cheaper than milk with the full-blown organic designation, which requires farmers to take the additional step of not spraying cattle feed with synthetic pesticides.

Pamela Bane, who had just finished shopping at the Whole Foods on Callowhill Street, said Friday she would not buy milk if the label said nothing about hormones.

"I watch the labels on everything. I don't want to feed my children all that junk, that man-made garbage," said Bane, who lives across the river in Sewell.

The Pennsylvania labeling changes would not affect the federal organic designation, only wording related to hormones.

Monsanto has lobbied for similar changes in other states, so far unsuccessfully; company officials say they've played no direct role here.