DO NOT SLAM ON THE BRAKE AND DO NOT PANIC. Slamming on your brakes will cause you car to skid. Swerving is not the best option as you could lose control of the car and crash. So, slowing down and not panicking will leave you with the fewest injuries on your body. Your vehicle could be affecting depending on the animal. If you hit an animal, put your hazards on a call 911.
Your life always comes before an animal.