I feed satin balls not only to my Labs, but the rescue Shepherds that I deal with daily. They are FANTASTIC for putting weight on a dog. Depending on the dog they can be mixed with kibble. Do a Google search and you can come up with grain free versions.
If your dog has digestive issues with mixing raw and kibble, give a satin ball as a mid-day treat or as a bedtime treat (separate from any kibble meal as much as you can). Kibble and raw digest at. Different rates, but I have not found much of an issue in more then 100 plus dog's that I have given that combination to.
to put weight on my youngsters that seem to burn through calories - I've both upped the fat content of the foods they eat and I've added cooked potatoes and oatmeal. this works for my dogs. Be mindful of this caloric increase as some dogs will gain quickly -
Barking Over The Moon made by SOlid Gold. It has 42% protein, grain free,. I also like raw but if you don't want to go that route try Barking Over The Moon.