You’d best be feeding that poor dog the recommended amount per day per weight of the dog. If you acquired that poor dog super skinny, you’d best be trying to get that dog to the proper weight as quick as you can.
A super skinny dog is not a healthy dog! Take your skinny dog to the vet & have it thoroughly checked out to make sure it doesn’t have a tape worm eating all the food that goes in its stomach! Tape worms are easy to get rid of too if that’s the case.
Also check the dog’s stool for parasites. Sometimes you can see them in the fecal matter & they are disgusting to say the least. They are easy to get rid of, too. But you’ve got to be on top of this asap before that poor skinny dog is no more! Good luck to you & your poor skinny dog. (source)