Why do most predatory mammals have more red blood cells per unit of blood then prey animals?

Answer 1

They don't. It's a simple matter of co-evolution. If predatory species started to evolve a higher concentration of red blood cells, prey species would co-evolve to have a higher concentration too. The final concentration of red blood cells is probably a compromise between oxygen carrying capacity and blood viscosity.

Seriously, people, read up on your subject before you ask questions. read more about co-evolution at http://en.wikipedia.org/wiki/Co-evolution

Answer 2

Because they need it to be stronger than prey anuimals.