A lactating dog may be eating for eight hungry little mouths, so she needs extra nutrition to keep her energy up. Since anything she eats gets shared with the nursing puppies, her diet should be monitored carefully to ensure that the quality and quantity of the milk remains suitable through weaning.
In the simplest explanation, calories equal energy. A lactating dog naturally burns more calories as she produces milk. The more the puppies nurse, the more milk she must produce. Lactating dogs become visibly fatigued while nursing. To keep your dog's energy up at the peak of nursing, she must eat an average of 300 per cent more calories than before pregnancy. The peak hits during the third and fourth week of nursing and continues through weaning. At that point, the puppies begin eating solid food and nurse less. In general, you should feed your dog about 150 per cent more calories the first week of nursing and 200 per cent more the second week. You may choose to feed your dog more of her current diet or select a new food that is higher in calories. Puppy food tends to be higher in calories than adult food. Avoid weight loss formulas.
Feed your dog a well-balanced diet filled with protein. If you switched your dog's food during the final weeks of gestation, then continue feeding her that diet, adjusting the quantity as needed. Choose a puppy formula food to provide the proper nutritional elements needed for both the puppies and the nursing mother. The first few ingredients should be meat with a lower quantity of wheat and corn (if any at all). Avoid additives and chemicals. Add cottage cheese or cooked eggs as needed. Calcium supplements should be avoided during gestation (pregnancy), and should only be used to boost the nursing dog's energy if needed. Consult a vet before adding any supplement to your dog's diet.
Nursing puppies stay hydrated entirely from their digestion of mother's milk, which can dehydrate the mother. A lactating dog should have access to clean water at all times and will consume a great deal more than usual. Lack of water can decrease the production of milk, which in turn dehydrates the puppies and may lead to other nutritional issues.
If your lactating dog receives enough food and water, she should not appear gaunt or thin. Her weight at weaning should be close to what it was when she was bred. If your dog is losing too much weight, increase the amount of food, switch to a higher quality food or add extra protein through eggs or cottage cheese. If her weight loss is extreme, you should take your dog to the vet immediately.