Richard Cotta, CEO of California Dairies Inc., the nation's second-largest dairy cooperative, is guided by a simple business philosophy: If you want milk with little blue dots, you'll have it, as long as you are willing to pay for it." So, when a string of major customers, including supermarket giant Safeway, came to his co-op saying they would no longer accept milk from cows treated with a genetically engineered growth hormone, the co-op bowed to the inevitable. In January, California Dairies' board voted to ask its members not to inject synthetic bovine growth hormone into their cows. The action by a co-op that ships 50 million pounds of milk every day is part of a sweeping, consumer-driven agricultural makeover. Demand for natural foods is rising, while increasing numbers of consumers are avoiding products that rely on antibiotics or growth hormones. And food retailers are listening. Recombinant bovine somatotropin, or rbST, was approved by the Food and Drug Administration 14 years ago. It sustains lactation by stimulating cows' appetites so they eat more and produce more milk, perhaps an extra 5 quarts per day. The European Union, Japan, Canada and Australia did not approve rbST. The reasons included questions about human and animal safety, as well social and economic considerations. Research that shows injections of rbST increase another hormone, insulin-like growth factor 1, or IGF-1, in cows. Too much IGF-1 in humans is linked with increased rates of colon, breast and prostate cancer. Synthetic hormone use also ... leads to increased use of antibiotics, whose overuse is already a serious problem in the livestock industry.