Puppies are born with the instinctive need to seek out their mothers, to find a nipple, and to nurse. This instinct ensures that they remain warm and that they drink colostrum. Puppies who fail to nurse shortly after birth may need assistance nursing so that they receive the benefits of this early breast milk.

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Puppies should nurse approximately every two hours for their first two weeks of life. Later, between three and four weeks old, you can start to wean them onto solid foods.
When do puppies start nursing?
After birth, the puppies' mother will help them out of their placentas and clean them for the first several minutes of their lives. Immediately after their mother is done cleaning them, most puppies instinctively will seek out a nipple from which to nurse. So, nursing starts pretty shortly after they are born.
Some puppies will be slow to seek out a nipple and can be guided gently toward one if necessary; as long as they are not vocalizing loudly and appear to be hydrated, it is all right to let these puppies find the nipples on their own. Puppies should nurse every two to three hours after birth. If they do not do so, bring them and their mom to the veterinarian to determine what might be wrong.
The benefits of colostrum for puppies

Newborn puppies do not have immunity to any diseases. The first breast milk that their mother produces is called colostrum, a thin, translucent liquid full of whatever antibodies she possesses. Drinking this colostrum will provide the puppies with passive immunity, that is, temporary immunity to the diseases the mother dog has been vaccinated against or for which she has developed natural immunity through recovery from them.
Puppies must consume colostrum during their first 12 to 24 hours of life. After this period, puppies' bodies can no longer absorb their mother's antibodies through the colostrum and it loses its beneficial effect.
Helping with puppy milk replacer
Although colostrum is beneficial for puppies, sometimes the mother dog is unable to nurse her puppies due to mastitis or another health issue. Or, if you find a litter of puppies without a mother, they'll need to get some nutrition into their bodies immediately to thrive. That's where puppy milk replacer comes in if you can't find another nursing mother dog.
Puppy milk replacer contains similar ingredients to a mother's milk, much like formula for human children. Mix up the puppy milk replacer as directed on the package and feed it to the little ones with a bottle or syringe. Note that cow's milk is not an appropriate substitute for growing puppies.
If you are hand-feeding newborn puppies, expect to feed them every three hours for their first two weeks of life and then every six hours for the next two weeks until you start weaning them.
How long do puppies nurse?
Puppies grow up pretty quickly and will only be nursing full-time from their mom for their first three to four weeks of life. After that, you can slowly start to wean them off of her milk and onto solid foods.
To easily transition them, you can mix a little puppy milk replacer into some dry kibble or wet puppy food to create a mushy meal that will tempt their taste buds. Expect feedings to be a little messy as the little ones muck around in their dish while they eat. By around eight weeks old, they should be eating puppy food exclusively.
Ensure mom gets the right food

While a mother dog is nursing her puppies and a couple of weeks before she gives birth, you'll need to provide her with a high-calorie food special for pregnant and nursing dogs. This will ensure that she has the nutrition she needs to properly nurse the pups. Don't keep feeding her this food after you wean the puppies though, as that could make her overweight.
- Royal Canin: What, and How, to Feed Your Pregnant Dog
- Dogster: Schedules and Guides for Feeding Puppies
- VCA Hospitals: Feeding the Nursing Dog
- American Kennel Club: Raising Newborn Puppies
- VCA Hospitals: Raising Puppies
- Vetwest Animal Hospitals: Orphaned Puppies - Caring, Feeding, Healthcare
- Revival Animal Health: Vet Minute: Why Colostrum for Puppies is Important