You cannot justify using animals for organs purely on the basis that we eat them. There must also be a substantial human benefit. As in many developments in biotechnology, we need to be wary of exaggerated claims and raising unrealistic hopes. Without putting it to the test, there is no assurance that animal organs would yield prolonged extensions of good quality life. We felt there was a case for trying, but with a proviso about animal welfare.
Pigs are sociable and highly inquisitive.
To rear pigs to be disease free might mean a very artifical living environment. There limits to how far we may use animals to replace human body parts. Beyond a certain point, either of animal suffering or poor efficacy, it would not be justified. There's an ultimate limit. Animals as Models of Human Disease Even more serious questions are posed by the commonest transgenic animals - genetically modified mice used as models for human genetic diseases or to test out possible therapies.