Milk is the answer to any newborn puppy's nutritional needs. However, this in no way means that just any kind of milk is suitable for a wee pup. Puppies need their mother's milk to ensure health and proper development. If necessary, puppy formula also can do the job.
Canine mothers begin nursing their puppies almost as soon as they are born. Until puppies are 3 to 4 weeks old, all the nutrition they need comes via nursing their mom's milk. When the mother dog decides it's time to start the weaning process, the litter gradually transitions from exclusively nursing to eating solid foods.
Not all litters of newborn puppies are lucky enough to have a nursing mamma in their lives. If a litter is orphaned, or if a mother dog is not well enough to adequately nurse her little ones, puppy formula and a commercial milk replacer can be a suitable replacement. Always use formula designed only for puppies if you must hand-raise a litter. A foster mother is preferable to hand-raising puppies if one is available who is willing and able to nurse the litter.
Other Kinds of Milk
Never feed newborn puppies any kind of milk other than a mother dog's milk or milk replacer formulated for puppies. Mamma's milk meets all of a puppy's diverse nutritional needs, and other types of milk just aren't suitable. Cow's milk is wrong for a puppy. The ASPCA says cow's milk can cause stomach upset and diarrhea in puppies. It doesn't matter whether it's standard milk from a carton, canned or powdered; stay away from it all.
If a mother dog has difficulty nursing her puppies for any reason, you'll know it by the loud cries of the hungry puppies. This is an emergency for your veterinarian to handle. The mother dog will need immediate attention to determine the cause of her problem, and the puppies must have nutrition. If the vet finds the mamma cannot nurse the litter, he may have puppy formula on hand, or you will find commercial puppy formula readily available at most pet supply stores. The product is easy to use. Just lightly warm the formula, following the package directions. When nursing issues occur, don't delay action. The mother's life may be in danger, and puppies can't live long if they're not nursing.