It is vital to make sure that your dogs are given the best nutrients during pregnancy up to the whelping stage. According to the American Kennel Club, a bitch makes use of her stored nutrition before and after her pregnancy thus it is important that she has enough supply of vitamins, minerals, and proteins that will support her body through these major changes. Malnutrition can cause physical abnormalities in her puppies. While obese or overweight dogs can run the risk of a difficult pregnancy.