Can we justify using animals as organ donors?

Recently, a pig kidney was temporarily connected to a human, and the first transplants of pig hearts in cardiac patients are on the way. Can we justify keeping animals and genetically modifying them for organ harvesting? For example, donor pigs must live a sterile life and cannot behave naturally. Wageningen philosophers will consider the ethical questions and look at how we can take the animal’s interests into account. Is it acceptable to further use animals as instruments for human purposes? What do you think about the moral component of using donor animals?