There were 33,600 organ transplants last year in the USA, and 116,800 patients on waiting lists and there are around one billion pigs in the world. 100 million pigs are killed each year in the USA for food.
A few tens of thousand of pigs grown for their organs would represent just a small fraction of that total, and that they would be used to save human lives. The animals would be anesthetized and killed humanely.
Harvard professor George Church founded a company, eGenesis, in hopes of selling the genetically altered pig organs. Eventually, Dr. Church says, the company wants to engineer pigs with organs so compatible with humans that patients will not need to take anti-rejection drugs.