When I first got my heeler (as an adult), he was thin and would not put weight on- he did turn out to have a pretty big load of worms, so I would start there! I have to worm him fairly regularly because he eats squirrels & rabbits that he catches, so I’m guessing ends up with tapeworms from their fleas (because HE doesn’t have fleas).
I’m on a budget but my dogs are on Merrick’s Whole Earth Farms, which I have found to be a great deal for a brand that’s rated 4 stars on here (was on sale at PetCo when I bought it last, 35lbs for $35). My dog is actually a heeler cross and is a little bigger, probably ~50lbs and eats 4 cups/day and looks great! Everybody here has lots of great suggestions, but I would definitely check about worms if he’s eating that much and still thin.
