What to do if my 4-week-old puppy won't eat or poop properly?

It sounds like the smaller puppy may have ‘failure to thrive’. This is especially common with puppies from large litters and not surprising since the mother dog is refusing to feed them. It sounds like the bigger pup is doing great and you don’t need to worry about him at all.

You should get a small scale (like a gram scale) so you can weigh the smaller pup everyday to ensure she is gaining weight. It is a little early but you could try to start introducing puppy food her as well. You can mix the canned food with milk replacer or moisten kibble with the milk replacer and see if she prefers this.

If she is not eating much it makes sense that she is not pooping as frequently. Continue to stimulate her to defecate several times a day. You should also have the puppies dewormed at this age as well.

If the puppy continues to refuse food after trying the above suggestions, you may need to take her to the vet to be examined. Your vet can also instruct you on how to safely syringe feed (or possibly tube feed) the puppy to ensure she is getting proper nutrition.

I hope this helps. Thanks for using Petco Pet Education Center, formerly Petcoach. Best of luck!