One of the most controversial GM foods is rBGH, or recombinant bovine growth hormone. The hormone, which is synthesized from genetically modified bacteria, produces higher milk yields by keeping milk-producing cells alive in cows for longer than normal. Though there's no official difference between rBGH milk and regular milk, critics point out that rBGH cows are more prone to disease, which means higher concentrations of bovine antibiotics filtering down into the milk supply.
The world is divided on whether milk from cows that were injected with recombinant growth hormones is safe. Though it's banned in the European Union and Australia, rBGH is legal in the United States, and there are no FDA requirements about labeling milk as coming from rBGH cows. Because of the controversy, many dairies and supermarkets advertise that they accept milk only from farmers who do not use rBGH.