Older dogs do lose weight - there's a period (of middle age?) where dog foods are tailored to keep old ones from from gaining weight, but as the end draws nigh, these poor animals just can't fatten up. One of our neighbors had a horse that was an incredible 40 years old or more, and people would report that horse to the county a underfed and neglected, when in fact only the greatest TLC would allow a horse to grow that old. As I recall, her owner claimed the old mare was close to age 50. I can hardly believe it, but it must be so. "Old bag of bones," indeed. Our own collie, Bailey, turned skeletal and so did our tough little neighbor dog Ted. At the end, he weighed so little, I could carry him like a cat. (Poor Ted!) So, yes, our skinny little senior dogs should have coats. :)