With buying from small, local, family-run farms becoming more popular, the results of a new study from Wisconsin could be surprising: It found that milk from big dairies is cleaner than that from small ones.

Lead researcher Steve Ingham said he did the study because he wanted to see whether there was a link between milk quality and the size of a dairy farm. He said the results cast doubt on the perception that big dairies can't matcher smaller ones in terms of quality.

"Certainly, the small-is-better blanket statement doesn't appear to be true," said Ingham, who started the study when he was a food science professor at the University of Wisconsin-Madison and is now a food safety division administrator at the Wisconsin Department of Agriculture, Trade and Consumer Protection.

But a group that represents small farms said the study was irrelevant because of the way it defined milk quality. It looked at the amount of certain cells and bacteria in milk, which are factors agriculture inspectors use to evaluate cows' health and farms' cleanliness.

Tom Quinn, the executive director of the Wisconsin Farmers Union, said the study ignored other aspects of quality, such as taste and nutrient levels. It also didn't address what he said are the real reasons smaller farms are better.

"I don't recall that we've ever claimed small farms are better because they produce more sanitary milk," he said. "Instead we've made that argument from environmental, economic and social issues."

The study published in the August issue of the Journal of Dairy Science used 2008 data collected by the Wisconsin government to look at levels of cells linked to mammary disease in dairy cows and bacteria tied to improper refrigeration or unclean equipment.

It found milk produced at large and extra-large farms had lower levels of both bacteria than that produced by small ones, although all the farms met standards for grade A milk certification.

Because he used data exclusively from Wisconsin, the nation's second-leading milk producer behind California, Ingham said he wasn't sure whether the results would apply elsewhere, especially in warmer states where bacterial growth might be harder to prevent.

He said the perception that smaller was better seemed to spring from the belief that small farmers have a greater incentive to collect milk hygienically and avoid taxing their cows with over-milking.

However, he noted, larger operators also have an incentive to keep their herds healthy, including by removing cows that have udder infections so they don't infect others. Bigger farms also keep bacterial counts down by investing in better sanitation and refrigeration equipment, he said.

Jayme Sellen, spokeswoman for the Dairy Business Association, which represents Wisconsin dairy farmers, said the study just shows that all dairies produce safe milk and consumers shouldn't be concerned.

"The main point is that milk is extremely high quality regardless of the size" of the dairy farm, Sellen said. "And that's not surprising. We have some pretty high standards here in Wisconsin. We know our milk."

The study defined small dairies as those with 118 cows or fewer and large ones as having 119 to 713 cows. Extra-large farms with 714 or more cows require special permits in Wisconsin.

Overall, Wisconsin dairies tend to be smaller, with an average of 88 cows in 2007 compared to California's 824, according to the latest federal statistics.

Several Wisconsin farmers argued that keeping smaller herds gives them an intimate perspective that's hard for bigger farms to replicate.

Darin Von Ruden, a dairy farmer in Westby, Wis., said he knew the personalities of his 40 cows so well that if one acted the slightest bit unusual he could keep her milk out of the general collecting tank until he knew what was wrong.

"That might not happen at the bigger factory farms," the 43-year-old said.

It's not clear how much that kind of thing matters to consumers, who often judge milk on its taste and shelf life. And since pasteurization kills most bacteria, consumers might not care as much about the data Ingham analyzed.

"I don't care about all that. Milk is milk," said Cherie Kappus, 58, a secretary in a Milwaukee law firm. "I just check the (expiration) date. Otherwise, it's all the same."

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Dinesh Ramde can be reached at dramde(at)ap.org.