More than half of U.S. milk is produced by 3 percent of dairies.

While milk carton imagery pictures bucolic, small farms, more than 50 percent of U.S. milk is now produced by just 3 percent of the country’s dairies — those with more than 1,000 cows, according to the U.S. Department of Agriculture (USDA). The very largest U.S. dairies now have 15,000 cows.

In Wisconsin, several dairy operations are now facing opposition to plans to expand their herds. Porous karst soils in the parts of Wisconsin where a significant portion of dairy expansion is occurring present some unique environmental issues. Run-off from dairy farms and other agricultural activities has seeped into aquifers and elevated levels of nitrogen, in some instances to unsafe concentrations.