The change was cheered by consumer advocates, who contended that farmers had a right to say - and consumers had a right to know - how their milk was being produced.

"It's basically a complete back-down," said Michael Hansen, a senior scientist at the nonprofit Consumers Union, which opposed the ban.

If dairies choose to advertise that they don't inject their cows, their labels will still require a disclaimer that their milk is no more safe to drink than that from injected cows. Such language already is found on milk at Whole Foods, Trader Joe's and some other retailers.

"The governor's position was relatively simple: He wanted the labels to be accurate and informative," said Rendell's press secretary, Chuck Ardo.

The debate marked a showdown of sorts at the intersection of free speech and the emerging world of biotechnology. The synthetic hormone, called Posilac and made by St. Louis-based Monsanto, is said to boost milk production by more than 10 percent.

It was approved by the U.S. Food and Drug Administration in 1994, but acceptance has been far from uniform. Monsanto officials say it is used on one-third of American dairy herds; the treatment is prohibited in Canada and Europe.

There is no proof that milk from injected cows is unsafe for people to drink. In enacting the ban in Canada, officials there cited the hormone's impacts on bovine health. According to the product label, the synthetic hormone increases the risk of mastitis - udder infection - and reduces the number of pregnancies. The company says these impacts are low-level; some scientists disagree.

The Pennsylvania debate began in October, when State Agriculture Secretary Dennis Wolff forbade any mention of hormones on labels, with or without a disclaimer, contending that it led consumers to think milk from injected cows was somehow inferior. Indeed, there is no proof that the two kinds of milk are different - though scientists say some questions about the hormone's effects have yet to be answered.

The issue has come up in other states. But Wolff's move would have been the first in the nation had it taken effect as planned Feb. 1, and it sparked a vehement reaction from consumers and some dairies, and resonated as far afield as Vermont.

There, ice cream maker Ben & Jerry's saw the ban as tantamount to a national restriction, saying that multistate retailers would be hard-pressed to print separate labels for Pennsylvania and for the rest of the country.

"Consumers care about what happens in the barn," said Ben & Jerry's social mission coordinator, Andy Barker. "They're not just buying a commodity when they're buying a gallon of milk or a pint of ice cream."

Ardo dismissed any suggestion that Rendell was at odds with his agriculture secretary, whose family was once in the dairy business and still owns a farm that specializes in Holstein genetics.

"The governor looks at things more broadly," Ardo said. "The review considered factors that hadn't been considered, such as the consumer's point of view."

Agriculture Department spokesman Chris Ryder said that a few consumers had input into the original decision but conceded that the agency received "a lot more feedback" after the announcement.

Asked how Wolff felt about Rendell's intervention, Ryder said the secretary was "happy with the resolution."

The rules also require that claims made on labels be backed up by a paper trail, subject to verification.

In addition to clarifying the allowable language for dairies that do not inject cows, the rules also prohibit the labeling of milk as "hormone-free." All milk contains hormones, whether natural or synthetic.

Todd Rutter, president of Rutter's Dairy in York, which supplies milk to 2,000 retailers in Pennsylvania and Maryland, praised the standards.

"I think it's a victory," said Rutter, whose dairy was among the larger producers fighting for the right to label.

Though there is no indication that bovine hormones themselves affect human health, some researchers have examined the impacts of a compound contained in higher amounts in milk from treated cows. High blood levels of that compound, IGF-1, have been linked with some human cancers, but the amounts in milk are far less.

Some consumers also have raised concerns that milk from treated cows can cause girls to reach puberty sooner. There is no evidence that this is the case, said Paul Kaplowitz, chief of endocrinology at Children's National Medical Center in Washington and author of the book Early Puberty in Girls.

There is a slight hint that milk of any kind could be linked to an earlier start to menstruation, said Marcia Herman-Giddens of the University of North Carolina's School of Public Health.

"It is a very growth-stimulating food," she said.

Text of the revised standard and scientific reports: http://go.philly.com/health