A person with such an attitude towards animals, sees humans the same way. He would have to.
Unfortunately, a head needs a donor body, right?
And you're not going to take a body banged up in a car accident, disabled, or available due to some disease, right?
So, reasonably, a donor would be ... whom?
A person with a mental disability?
A person having suffered severe head trauma?
A person with an expected lower standard of living than the recipient head?
Or maybe a clone of the person? Except that, that would require some advance planning, a clone willing to sacrifice, and of course an answer to the question: why not just transfer the consciousness instead of the whole head.
It just seems that such an act of experimental barbarism should have the whole thing clearly thought out.