This fact about cow's milk is a bit hard to swallow...
"According to the USDA, 1 in 6 dairy cows in the United States suffers from clinical mastitis, which is responsible for 1 in 6 dairy cow deaths on U.S. dairy farms. This level of disease is reflected in the concentration of somatic cells in the American milk supply. Somatic cell counts greater than a million per teaspoon are abnormal and "almost always” caused by mastitis. When a cow is infected, greater than 90 percent of the somatic cells in her milk are neutrophils, the inflammatory immune cells that form pus. The average somatic cell count in U.S. milk per spoonful is 1,120,000.
So how much pus is there in a glass of milk? A million cells per spoonful sounds like a lot, but pus is really concentrated. According to my calculations based on USDA data released last month, the average cup of milk in the United States would not be expected to contain more than a single drop of pus.
As the dairy industry points out, the accumulation of pus is a natural part of an animal’s defense system. So pus itself isn’t a bad thing, we just may not want to have it in our mouth.
And you can taste the difference. A study published in the Journal of Dairy Science found that cheese made from high somatic cell count milk had both texture and flavor defects as well as increased clotting time compared to milk conforming to the much more stringent European standards. The U.S. dairy industry, however, insists that there is no food safety risk. If the udders of our factory-farmed dairy cows are inflamed and infected, industry folks say, it doesn’t matter, because we pasteurize—the pus gets cooked. But just as parents may not want to feed their children fecal matter in meat even if it’s irradiated fecal matter, they might not want to feed their children pasteurized pus."
From Dr. Michael Greger, www.nutritionfacts.org