According to this article, scientists have succeeded in creating a sheep that is composed 15% of human tissue. It reminds me a little bit of books and stories that I have read. If you want to read a bit more about this sort of thing, in the science fiction realm, read on.
You might find this book interesting: The Illegal Rebirth of Billy the Kid, by Rebecca Ore. It is about "dog meat robots", chimeras, the times, rights and lives of artificial people made of initially-dog-sourced DNA. It starts out somewhat silly, but becomes quite ominous. Another author, Octavia Butler, does a much less cyberpunk and rather more serious treatment of DNA mixture (this time by aliens), in a trilogy that starts with Dawn.
news story ganked from ironkite