If you're in charge of caring for a newborn puppy, then you have a lot of responsibility on your hands, especially if the mother dog isn't available for nursing. When it comes to feeding pre-weaned puppies, the only suitable and healthy options are the mother dog's milk or puppy-specific formula.
Nursing
If your newborn puppy still is with his mama, then at first you do not have to do anything in terms of feeding him, unless the mother is ill and can't nurse, of course. The mother dog's milk can manage all of a young puppy's diverse nutritional needs, with no outside assistance necessary. Until the mother begins weaning her little one off of nursing at around 3 or 4 weeks, the puppy won't require any solid foods at all.
In the event that the mother dog isn't around or is not able to nurse, use a commercial milk replacer to nourish the puppy. Make sure only to use formula made specifically for puppies.
Cow's Milk
According to the Virginia-Maryland Regional College of Veterinary Medicine, milk from a cow is not appropriate for puppies. A mother dog's milk is very different than cow's milk, and puppies usually do not digest the latter very well. Cow's milk often results in stomach upset in pups, and unpleasant and uncomfortable diarrhea to boot. Thanks, but no thanks. Spare your poor pooch the distress and leave all forms of cow's milk out of the equation.
Canned and Powdered Milk
Canned milk and powdered milk are cow's milk, although in slightly altered forms. Canned milk involves the extraction of water, while powdered milk is simply evaporated. Avoid feeding either of these beverages to a puppy. Not only can these cow's milk products lead to digestive upset, they aren't balanced to accommodate the extremely particular dietary requirements of a puppy. Puppy-specific formula consists of the proper balance of amino acids, minerals and proteins that the youngsters need to thrive and remain healthy.
Canned and Powdered Puppy Milk Replacer
Although canned and powdered cow's milk are major "no nos" for a puppy, you may notice that puppy milk replacer comes in canned and powdered versions. As long as a product is labeled as being formulated exclusively for puppies, you should be good to go. If you're uncertain about any products with regard to your puppy, consult your veterinarian. Just remember that puppies have absolutely no use for any type of cow's milk -- no exceptions to that rule!