Considering puppies have neither the ambitious potentials nor life expectancy a baby does, it's not equivalent. You can think of it as comparing the death of a retired 60 year old man who has 20 years left to live and the death of a newborn baby. Life is life, and preserving it in any case is an important issue, but to consider it as an equivalent to a baby is to take it to another extreme.
I don't think that ambition or potentials should have any affect on how somebody is punished for a crime. I think that every life is more or less equally important, whether or not they expect a long life.
When you murder somebody, do they look at how much longer the person expected to live? Is there a shorter sentence for murdering a smoker or a fat person?
I agree that preserving life is important, but I'm trying to raise the point -- if this was a baby, the guy would probably have gotten life in prison (minimum 10 years, I bet), whereas people are upset about getting 3 years for a dog. I don't see why killing an animal (any reasonable animal) should be any less than a human. Sure, they won't change the world, but neither do most people. I've decided that, from a utilitarian point of view, an animal losing his/her life is as bad for the animal as a human losing his/her life is for a human.
It's really a matter of opinion, though.