What is the best thing to feed my dog to help her gain a little weight.?

Make a delicious homemade dog food of white rice, ground beef & carrots (cooked). Give it to him once a day Always keep some dry dog food like Beneful out so the dog could eat whenever he is hungry & don't forget that extra biscuit or beggin strip. (That should add some weight.) Make sure that the pup is happy & warm. (If a dog is not happy they won't eat) See the Vet! Good luck!