I'm not a breeder either, but have two new babies.
I started feeding my mom to be cooked chicken, beef (which we raise) and venison along with the puppy food. I used Royal Canin puppy and just kept it out all the time for her. She got as much chicken/beef/venison as she wanted three times a day and believe me, the farther along she got, the more she scarfed up. Fed her a little buttermilk too. After she had her babies, she got so skinny, but the vet said that was to be expected and to keep her on the puppy food and give her whatever she wants. I give her Nutrical too.