
That is because in the first three days she needs to be nursing almost constantly for the demand to cause supply.
Don't expect to see milk though, some bitches don't bag up, but still produce the amount needed.
After a C section pups may be too sleepy to provide enough stimulation.
If pups have not regained their birth weight and started to increase by the third day tehn you will need to top up a bit, but only after they have fed so that the demand of suckling increases her production.
The section can also slow down the milk coming in.
Put pups on the teats constantly, even if you have to wake the pups.