Not exactly milk and honey

Livestock animals have the capacity to synthesize large amounts of recombinant proteins, making them good candidates for protein factories. Most such work has focused on production of proteins in the milk of transgenic animals, but milk isn't the only fluid that animals produce.

Researchers at New York University and the USDA published in Nature Biotechnology the generation of transgenic mice that express human growth hormone (hGH) in their bladder epithelium and secrete the hGH into their urine. In contrast to milk, urine is relatively free of other proteins and lipids, making purification of the recombinant product easier. Also, urine is produced by animals of both sexes throughout their lives, rather than during lactation periods in mature females...