On the first question, yes I don't see a problem (aside from the whole issue of people who are willing to donate stem cells for money would probably much prefer

On the first question, yes I don't see a problem (aside from the whole issue of people who are willing to donate stem cells for money would probably much prefer to have their financial needs met without requiring a medical procedure). On the second question, yes I think there is a slight difference since animals can't consent. If the question is strictly "would you rather do a biopsy on a cow or a consenting human" I'd choose the human. I'd think most people would agree on the rule "don't hurt a person unless you have a good reason". Vegans just extend that to "don't hurt an animal (the kingdom) unless you have a good reason". And to me, informed consent free from coercion is a good reason, but taste is not.