
I have had bitches with pups gaining weight extremely well, that never bagged up and showed milk obviously but of course had plenty for the puppies.
For the first three days pups need to virtually be on the bitch no stop to bring the true milk in, as it works on demand and supply. Any woman who has breast fed will be familiar with that feeling of waking up feeling like a load of bricks are on your chest, on about the third day when the milk comes in.
The pups weight gain is your clue to everything being as it should be. No gain in the first day or a small loss in medium to large puppies, especially bigger litters is normal, just Monitor for hydration and keep plugging pups on.