People have said it, but I will say it again. Before you kill anything make sure the reader cares about it.
Also think about the tone of your story. Lots of blood gives you a splatter movie feel, that's not a subgenre that is known for being able to evoke a deep sense of loss, and for good reasons it doesn't have a literary analogue.
What you want to make it sting is the moment of connection. The moment when you look in the dog's eyes and the dog looks back at you. You know the dog is going to die, and the dog knows you know, and then it's over.