one of my first litters was very hard to wean , showing little interest , holding out for mums milk!
i took advise from a little old lady who had bred pups for many years
she said go to the butchers get a good steak , chop it up as small as possible
feed raw ,just for 1 or two meals then mix a tiny amount of steak into a complete puppy food just for a day or two, i have followed this advise on all litters from then on
the pups rush to the plate every mealtime just in case the steak was on offer
again !! the plate is empty every time ! mums milk dries up much quicker as the pups are full of solids
its makes sence to me as in the wild a bitch would offer a simular food
give it a try