pharming (färˈmĭng) [key], the use of genetically altered livestock, such as cows, goats, pigs, and chickens, to produce medically useful products. In pharming, researchers first create hybrid genes using animal DNA and the human or other gene that makes a desired substance, such as a hormone. Employing the techniques of genetic engineering, they then introduce the hybrid genes into animal embryos, which are then reimplanted into foster mothers and carried to term, creating transgenic animals that secrete human hormones or proteins, antibiotics, or other substances in their milk, blood, semen, eggs, or the like. The material containing the secreted substance is harvested, and the substance extracted and purified. The process has yielded drugs, such as growth hormone and antithrombin; blood components, such as hemoglobin; and large quantities of certain proteins needed for research.
Still largely in the developmental stage as a manufacturing process, pharming must overcome technical and economic hurdles, and substances produced as treatments for human beings also must be tested in clinical trials. Nevertheless, it is regarded as a more efficient alternative to the technique of using genetically altered bacteria or specially cultured animal cells to produce drugs, and as the only way to produce some more complex proteins. Also being experimentally explored is the use of genetically engineered plants, specifically rubber trees, to produce pharmaceuticals in their sap and the use of transgenic animals as sources of organs for medical transplantation. A necessary step toward the later was achieved in 2000 when pigs were cloned that lacked a gene that causes the human immune system to reject swine tissue.