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.
In an interview, state Agriculture Secretary Dennis Wolff said he ordered the changes after hearing repeatedly from people in the dairy industry. He once used the hormone on his own dairy farm, though his family got out of the business in 1999.
Wolff said his move was prompted by several concerns. Among them: the inaccurate "hormone-free" labels that were uncovered in a departmental review, and other labels claiming that the milk came from cows not treated with rBST.
Those labels wrongly imply that other milk - from treated cows - is less healthful, he said. And with no commercial test to tell the difference between the two, consumers don't know if the packaging is accurate, he said.
All references to hormones on milk labels were banned in Pennsylvania under the new standards, announced Oct. 22. After the move sparked a heated debate, Wolff delayed the Jan. 1 start date by one month for a review.
"Is there labeling that informs the consumer without implying that it's a safer product?" Wolff said. "That's what we're looking at right now, and trying to determine if there is language like that that may be acceptable."
For those who study effects on human health, the main issue is not bovine growth hormone itself. Neither the natural nor the synthetic version is "bioactive" in humans.
The research has focused on another protein found in milk: insulin-like growth factor 1.
IGF-1 also is naturally present in the blood of cows and humans, in identical form, and at high levels it has been associated with certain human cancers.
And people who regularly drink milk have somewhat higher IGF-1 levels in their blood.
Yet these increases are very small compared to the natural range of human IGF-1 levels, said oncologist Michael Pollak, director of McGill University's Division of Cancer Prevention in Montreal.
As for a possible cancer link, he said, "there's no real smoking gun."
But a question remains:
In milk from cows treated with synthetic hormones, levels of IGF-1 can be even higher - by 25 to 70 percent, according to a 1999 review by a European Union scientific panel.
So does milk from hormone-treated cows - with the higher IGF-1 levels - have an even greater impact on the IGF-1 blood levels of people who drink it?
The answer is not simple.
Scientists disagree on whether any of that IGF-1 in milk survives the human digestive process and ends up in the bloodstream - or whether all the IGF-1 found in people is made by the human body.
In one study, researchers placed radioactive markers on IGF-1 and fed it to rats; they later detected the markers in the animals' blood. The amounts were even higher when the rats also were fed casein, a milk protein.
Mike Lormore, a doctor of veterinary medicine at Monsanto, was skeptical of that result. He said that the growth factor might have been digested and the markers continued into the blood on their own.
Janet Rich-Edwards, an epidemiologist and assistant professor at Harvard Medical School, called the matter "unsettled."
There is no dispute, however, that Posilac can affect the health of cows. The product label cautions that injected cows are at increased risk of mastitis and "may have reduced pregnancy rates."
A review by Health Canada - that country's equivalent of the FDA - estimated an 11 to 19 percent increase in mastitis, which is treated with antibiotics. Monsanto's Lormore said the increase was small when compared to other mastitis risks such as poor sanitation.
"Just like if you pick up some Tylenol, there's a label with everything known to man that can possibly ever go wrong with Tylenol," Lormore said. "The risk of those side effects is deemed to be very low and manageable."
As of now, the new Pennsylvania standards will take effect in February. And Harnish, the Lancaster County farmer, is happy with the change.
"There's something to be said for truth in labeling," Harnish said. "But I think we have to be real careful that the labeling does not imply something that's not true."
Pending standards for synthetic hormones in milk, scientific reports and additional background:
Contact staff writer Tom Avril at 215-854-2430 or firstname.lastname@example.org.