During lactation, your mama dog's nutritional needs are even higher than they were during pregnancy. Until those puppies are weaned, she's still eating for five, or six, or seven ... so you should continue giving your dog many of the same types of food you fed her during her pregnancy as long as she's nursing. Always check with your vet regarding your nursing dog's diet.
Once your dog gives birth, she'll drop some of her weight, but she'll need two to three times as much food as she consumed before pregnancy. Because of her nutrient and caloric needs, rather than feeding her larger amounts of her standard dog food, give her a top-quality puppy food. Since you have it on hand, it's also easy to put some aside for the puppies as they begin eating solid food, usually at about the age of 4 weeks. Don't feed a nursing mother a large-breed puppy food, even if she is a large breed. Those formulas don't provide sufficient calcium because of risks of abnormal bone development in large-breed puppies. Because your mother dog produces so much milk, she always needs fresh, clean water available. Check the bowl often because she's probably drinking a lot more than usual.
Mother Dogs' Needs
Your nursing dog requires more calcium and phosphorus, both for the bone development of her pups and her mineral depletion through lactation. Her puppies also require protein to develop, which she must provide. Nursing dogs require four to eight times the energy requirements of normal adult dogs, according to Hill's Pet Nutrition. Feeding your dog additional healthy fats can satisfy these needs and easily add calories. Top milk production occurs when the puppies are 3 weeks old, corresponding with their nutritional needs at that stage.
Ask your vet about the amount of food you should feed your nursing dog. Depending on the breed, number of puppies and other factors, your vet might recommend that your dog have food available at all times. She'll definitely require feeding several times a day, rather than the once- or twice-daily schedule of typical adult dogs. You should visit the vet on a regular basis with the puppies, so she'll weigh your dog and advise you if she thinks your dog requires additional nutrition.
Even if you normally feed a homemade or raw diet, when your dog is nursing it's best to go with a commercially prepared food. According to the ASPCA, a nursing mother has special nutritional needs, including vitamins and minerals, that a homemade diet might not meet. Raw diets contain bacteria that might not bother a dog with a healthy immune system, but remnants of the mother's food could affect puppies with immature, fragile immune systems.