Most large breeds of dogs can feed 12 puppies quite well. But you will probably need to help the mother along by giving her extra food as long as the puppies are nursing. Most dams will need two to three times as much food as they consumed before becoming pregnant.
As a general rule, feed 150% of the maintenance energy requirement during the first week of lactation, 200% of maintenance during the second week, and 300% of maintenance the third …