The correct answer is: it depends.
It depends on the size of the animal, your speed and most important, the traffic around you.
Let's say you are only a busy divided city street, a dog runs in front of you and traffic around you is heavy. You have no choice but to hit the dog assuming due to traffic it's dangerous to brake hard. But if you are on a lightly traveled country road and a dog runs into the road, if you are not traveling too fast, you may be able to avoid the animal.