If you have orphaned puppies, either because the mother is ill or refuses to nurse her babies, it's up to you to give them the nourishment they need to thrive. Puppies eat often, although the frequency slows a bit by the time puppies hit 3 weeks old. Still, be prepared to get up during the night to feed them all.
Newborn puppies need to eat about every two hours, but you get a bit of extra time between feedings when the puppies are 3 weeks old. At that age, they need to eat about every four hours. It only takes a few minutes to feed each puppy, but with litters that can sometimes be eight or more, block out at least an hour to mix and heat the formula and feed each puppy individually. With large litters, recruiting an assistant can help make the feedings go faster.
Amount of Food
The amount of food you give varies by the size and breed of your puppy, but a basic rule is to feed them a little less than they want. Their tummies should be full, but not bloated or distended. If you notice formula coming out of a puppy's nose, stop feeding him; he's had a bit too much. When their bellies are full, the formula can cross over into their lungs. When this happens too often, they can end up with dangerous pneumonia.
What to Feed Them
Puppies don't handle cow's milk like humans do, so don't give them milk or mix a powdered formula with milk. Cow's milk can upset their tummies, sometimes giving them serious diarrhea. Instead, use a canine milk replacer, which is available at pet supply stores or some veterinarian offices. You can buy the milk replacer in cans of ready-to-eat liquids or in powder form that must be mixed with water. Heating the formula slightly above room temperature is more natural for the puppies and helps them regulate their body temperatures.
How to Feed Them
Three-week-old puppies are almost ready for regular food, but not quite. You can put their formula in a shallow dish to give them an opportunity to learn to lap it up, but not all puppies of this age can quite get the hang of it. Bottle-feeding is still best for another couple of weeks. To feed a puppy, put him on a solid, level surface such as a table. He would normally have all his feet on the floor if he was nursing from his mom, so this is a comfortable position for him. Place the bottle's nipple in his mouth, pulling back slightly if he gets distracted from eating. The bottle should be tilted slightly up at an angle so only formula is in the nipple; any air that ends up in the nipple also ends up in the puppy's belly. When he's finished eating, hold him upright against your chest to burp him, just like you would a human baby.