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.

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.