Anything you might imagine -- bigger, stronger, faster, smarter, better eyes, ears, nose, teeth, camouflage or endurance, more hot, cold, wet or dry weather adaptations, etc., etc.
Indeed, when humans first began to develop new breeds of domestic animals and plants -- thousands of years ago -- the only thing they did was replace evolution's "natural selection" with "human selection".
The results illustrate the whole idea of evolution's "punctuated equilibrium", meaning species can remain apparently unchanged for millions of years, and then "suddenly" evolve into something quite different looking.
Of course, a few thousand years is not enough for mutations to create a new "species boundary" (as annalex calls it) between breeds.
But human animal husbandry shows us how quickly species can change under the right conditions.
