My dog is a 12-year-old purebred border collie. In the past year or two she has started to thin out. In fact, you can feel her spine. My dad changed her food a couple of months ago and she filled out a little bit again, but the food is crap. I have been doing a lot of research on pet food lately and i'm going to try and talk to him about changing her to a more healthy diet. What would cause a dog to shed weight like that? She's been healthy for most of her life so i'm not sure what would cause it to happen. The dog is my dad's responsibility so I don't deal with the vet bills for her, but I'd like to know what's wrong. Any suggestions?