The link above goes to an article about the development of human-sheep chimeras. I will add to this post later, but for the non scioentists who read SJ, there is an issue beyond morality. That issue is exo viruses.
Viruses are parasitic. That means they generally are adapted to not harm the species they infect. These chimeras could "tech" an animals virus how to nfect humans. Something like this happened already ... HIV!