A transgenic animal is an animal in which one or more genes have been introduced into its nonreproductive cells. The first transgenic animal was produced in 1983 when genes for human growth hormone were introduced into mice.
Transgenic animals can be used to produce valuable products. For example, a transgenic pig has been produced with the ability to synthesize human hemoglobin for use as a blood substitute. Also, a transgenic cow has been bred with the ability to produce human lactoferrin, an iron-building milk protein and a potential antibacterial agent. A transgenic sheep can synthesize a protein that helps emphysema patients breathe more easily, and a transgenic goat has been developed to produce a protein needed by cystic fibrosis patients.