you're totally describing MY GSD, Jaida. She's got "shepherd stomach" too, whatever that is, and she's historically been a TERRIBLE eater, and it's very hard to keep weight on her. She also vomits pretty easily, and will vomit almost for sure if she goes more than half a day without food (some dogs can eat once a day, but she needs two meals or else she gets the yellow biley barfs pretty easily). I had to chuckle a bit at the "gravy drippings, canned meat etc. etc." attempts to get your guy to eat because OMG we've been there. There were days where the only way we could get her to eat ANYthing was basically to hand feed her tiny licks of food
That was Jaida about, oh 8 months ago.
Now when it's meal time, she's pretty much the first to her plate, she never
turns up her food, she eats every last bite with gusto, and we've been able to flesh her out a bit for the first time.
Our "miracle cure"? Raw food. We switched the dogs to an entirely raw diet (raw meat, bones, organs, with occasional bits of fruit and veg mainly as treats, but pretty much 98% meat etc.) Jaida took to it IMMEDIATELY and hasn't looked back. If you've tried everything else, I seriously recommend that you look into raw. You may find that you have to feed a fair bit of food (Jaida eats about twice as much as our other large dog in order to sustain her body weight) if your pup is a "poor keeper" like ours, but I tell you it's worth it to not have to beg her to "EAT PLEASE FOR THE LOVE OF PETE EAT SOMETHING" every. single. day.
Solomon - black DSH - king of kitchen raids (11)
Gracie - Mutterooski X - scary smart (9)
Jaida - GSD - tripod trainwreck and gentle soul (4)
Heidi - mugsly Boston Terrier X - she is in BIG trouble!!! (3)
Audrey - torbie - sweet as pie (11 months)
Patrick - blue - a little turd (but we like him anyways) (6 months)
Boo, our Matriarch (August 1 1992 - March 29 2011)