The Physicians Committee for Responsible Medicine (PCRM), a health advocacy organization, explained in its article "What's Wrong with Dairy Products?," published on their website (accessed Mar. 26, 2007):

“Synthetic hormones such as recombinant bovine growth hormone (rBGH) are commonly used in dairy cows to increase the production of milk. Because the cows are producing quantities of milk nature never intended, the end result is mastitis, or inflammation of the mammary glands. The treatment requires the use of antibiotics, and traces of these and hormones have been found in samples of milk and other dairy products.”

Mar. 26, 2007