
Hi Claire, you could be describing an Irish Setter I had in the past. He too was a bag of bones, very very windy, but really active, rarely poorly, very happy in himself, just very very thin. I used to say you could play the piano on his ribs. My husband used to say that the RSPCA could be forgiven for thinking we didn't feed him. He was a fussy eater as a puppy, but became better over time, but he wouldn't allow me to feed him up though
I think you are right to have your boy looked at by the Vet, I just was of the opinion that Cassidy was healthy enough because he was happy active and never ailed anything. At 5 years old, I lost him to bloat, I'll never know whether there was something the Vet could have diagnosed earlier.
I haven't told you all this to frighten you, just to encourage you to take Fagin to the vet, I'm sure he'll be fine, I have regrets about Cassidy, you don't need to have them too. :)
Dawn R.