But every month, 300 gallons of the milk are sold raw, much of it to about five dozen regular customers who arrive at the central Illinois farm toting their own containers to tap the creamy drink from a squat, stainless-steel vat in a room next to the milking stalls.
The federal government and virtually all public health agencies oppose consumption of raw milk because it can carry dangerous bacteria including E. coli 0157:H7, listeria and campylobacter. Last month, 13 people in Michigan were sickened by campylobacter in an outbreak tied to raw milk sold at a northern Indiana farm.
Raw milk drinkers argue that they should be allowed to decide whether to take the risk. Many who drink raw milk believe the unprocessed, nonhomogenized version is more nutritious and can help with ailments such as allergies, asthma and gastrointestinal issues, though public health agencies and nearly every major medical association in the country say those benefits are unproven.
"It's more than a health issue; it's a human rights issue," said Kathryne Pirtle of Addison, a professional musician who credits raw milk with eliminating the chronic pain she experienced for 25 years. "Real food and the raw milk movement are the answers to our health care crisis and the future of our populations."
The FDA bans interstate sales of raw milk, but states regulate its sale within their borders. Sales are now legal in 27 states under some circumstances, with bills to legalize it pending in Georgia and Wisconsin. In several states, including California, Connecticut and Pennsylvania, raw milk can be sold in retail stores.
In Illinois, consumers who want raw milk must take their own containers directly to the farm. Another option is a cow share, in which a consumer contracts with a farmer or "milk club" operator to buy a share of the animal. As part-owner, the customer is entitled to some of the cow's milk.
Some suspect these arrangements, which are not regulated or inspected in Illinois, may be one reason that federal officials are cracking down on raw milk sales, stepping up efforts to warn consumers of the dangers and urging states to strengthen their regulations.
Parrish and O'Shaugnessy raised four children on raw milk and are avid proponents of its virtues. Though the Wisconsin company that purchases the farm's regular milk (about 2,000 gallons a month) recently said it would stop buying unless the couple ceases selling raw milk, they vow to continue.
"Consumers have a responsibility to decide what they will put in their mouths," O'Shaughnessy said. "It isn't our goal to convert everyone into drinking raw milk. We're not evangelists. We're just farmers."
From 1998 to 2008, 85 outbreaks of human infections resulting from consumption of raw milk were reported to the Centers for Disease Control and Prevention, including a total of 1,614 illnesses, 187 hospitalizations and two deaths.
The outbreaks about five per year over the last few years are due primarily to campylobacter, salmonella and E. coli, according to Robert Tauxe, deputy director of the CDC's food-borne and bacterial diseases division. "We view it as an ongoing problem, one that puts everyone who drinks raw milk at risk," he said.
Drinking contaminated raw milk can cause vomiting, diarrhea and abdominal pain. Most healthy people recover quickly, but the bacteria can be especially harmful for pregnant women, the elderly, children or those with weakened immune systems.
What confounds health officials is the sense that the more they warn against raw milk, the more people seem to want it. In addition to the supposed health benefits, drinking raw milk is seen as a way to support local farmers and bypass the industrial food chain.
"In America we've lost our sense of community, and we're trying to re-establish ties to that which sustains us," said Tim Wightman, founder and president of the Farm-to-Consumers Foundation and the author of the Raw Milk Handbook, a resource guide for farmers. "Raw milk is the gateway; it allows us to begin to question everything we call normal.' But this is widely misunderstood by governments and corporations."
Wightman says raw milk drinkers run the gamut from older farmers and hippies to doctors who drink it in secret. But health-conscious mothers are the core group pushing sales these days, he said.
Jill Cruz of Chicago was already eating organic when she first looked into raw milk. Her 4-year-old daughter, Sonia Rose, had a cavity, and Cruz wondered whether the cause was a nutritional deficiency. Safety is not a concern, she said.
"No food is 100 percent safe," said Cruz, the leader of the Chicago Chapter of the Weston A. Price Foundation, a raw milk advocate. "I don't think anyone out there can guarantee that."