One of the earliest applications of biotechnology was the genetic engineering of a growth hormone (bovine GH) produced naturally in the bovine pituitary. Bovine GH can increase milk production in lactating cows. Using biotechnology, scientists bioengineered the gene that controls bovine GH production into E. coli, grew the bacteria in fermentation chambers, and thus produced large quantities of bovine GH. The bioengineered bovine GH, when injected into lactating cows, resulted in an increase of up to 20 percent in national milk production. Using bovine GH, farmers are able to stabilize milk production in their herds, avoiding fluctuations in production levels. The U.S. Food and Drug Administration (FDA) approved use of recombinant bovine growth hormone in 1993 after ten years of study. A similar regimen was adapted using the pig equivalent of growth hormone (porcine GH). Injected in pigs, porcine GH reduced back fat and increased muscle (meat) gain. Pig growth hormone has been test marketed in a select population with no ill effects; however, it has not yet been approved by the FDA.

The first transgenic animal available as a food source on a large scale was the salmon, which reached U.S. food markets in 2001, following rigid evaluations of consumer and environmental safety. These salmon have the capability of growing from egg to market size (6 to 10 pounds) in 18 months, as compared to conventional fish breeding, which takes up to 36 months to bring a fish to market size. The use of transgenic salmon can help reduce overfishing of wild salmon stocks.