I have been bottle feeding a pair of puppies who were rejected by their mother since birth. This past week one of the puppies has begun to reject the bottle, or barely even tries to eat and sleeps most of the day. While the other continues to eat well and is very active. What can I do to motivate this little guy to eat?

Are they healthy? The mother OFTEN rejects them because she senses they have a health problem.

How can I motivate the puppy to eat?

Are they healthy?

Have you tried mush made with puppy kibble?

Puppies dehydrate and starve very quickly - how long have they not been eating?

If these are infants, I don't think mashed puppy food is what they need...

Like Judy said, rejected puppies are typically rejected for a reason... Call your vet... That pup needs medical intervention if you are interested in saving this puppy.. however, their might not be a guarantee that a vet visit is going to save it :(

Harsh reality of breeding animals..

I tend to agree with Judy, Mother Nature has a way of letting mothers in the animal kingdom know if something is wrong. If the pup seems healthy and has been doing well up to this point then you may be dealing with a developemental issue, but if you are like myself and are bound to do your best to care for him.
1. Make sure he stays warm, puppies cannot regulate their own temperature at this point so you must make sure their living quarters are kept cozy.
2. When pups are not eating well, their blood sugar can drop, causing them to become sort of "floppy" and listless. If this happens he will need a simple sugar like Karo syrup, if that is not available at the time you can even use pancake syrup. Just rub a little on the gums and tongue, do not pour or syringe it into the mouth, it will be too easy for them to aspirate it into their lungs. If the immediate problem is blood sugar you will see improvement quickly.
Keep in mind that the sugar is only a temporary fix, if there is something else going on all the sugar in the world won't fix it.

I hope that this is just a hurdle for you and that the outcome is good, but try to keep in mind that he may not make it, and that won't be your fault.

Best wishes

While I agree these pups need to be checked for any health problems there are a lot of mothers who simply just don't "get it" with their own puppies and refuse to care for them. My friend had a litter of 3 bouncing baby shih tzu pups new years eve and the mother wants nothing to do with them... they have all been checked and are fit and healthy.

At 4 weeks they are definitely ready to start on solid foods. Soaked puppy dry food mashed up or a little bit of canned food is a good start, just mix it up with the milk you are already feeding and offter it to them on the end of your finger, or even dab a little on the end of the bottle to encourage them to try it.
Only a tiny amount at first to avoid constipation or diarreah.

If the pup refuses both the bottle and the solid food then you can also try some appetite stimulants. These are available from your vet so you can get the pup checked out at the same time.

It may have an illness I think you have to get it checked or any traces of illness.