What to possibly use and how to feed puppies ONLY after discussion with your veterinarian:

Used by someone very experienced with ME puppies and getting them to resolve their ME: “With puppies, I have fed watered down, mashed dry kibble. I add to that a number of things for extra calories, such as canned pure pumpkin, baby cereal flakes, coconut oil, pureed baby food, etc. to make it a milkshake consistency. They really do get all the water they need from this, but you can also add Thick-It to water to give them. Walgreen’s has their own brand, which is cheaper and works just as well. Upright time after feeding is a necessity. I have used a baby walker, a front-pack carrier or simple holding them up over your shoulder while you walk around doing chores. Nothing by mouth” pertains to crumbs left on the floor or free standing water. Those tend to be the culprits for these puppies.”

Here are some questions and answers from an ME  owner and answered by another experienced ME owner. This is an example and must be discussed with your veterinarian.
1.  How many times a day to feed her
At that age, I’d feed every 3 hours

2.  Amount per feed??? Less or normal?
This varies a lot, start with lower amounts and work up, sometimes it takes work to get them to tolerate much.

3.  Wet food ? Harder ????? My vet said kibble?
No kibble! Kibble stretches the esophagus out especially in puppies. I find for the 2 ME babies I’m raising here what works best is either firm canned food, or blending canned food with water and gelatin and then letting it set up until firm in the fridge, and giving in small meat balls. But every puppy is different. ME
puppies I’ve had in the past some did best on REALLY liquidy food, some did best on thick pudding like consistency, some did best with straight canned or meat balls, it’s kind of trial and error. You want it as smooth as possible so it slides right now, but other then they it’s kind of an experiment to see what works for that
individual puppy.

I would still use formula at 4.5 weeks with the canned food. The prescription diets that are highly digestible work really well for the ME dog. You want a formula that will digest easily and leave the stomach. We had a litter of parvo pups who weren’t even weaned (not me but needing special care) and the prescription diet and formula helped get them on the road to recovery. The diets aren’t cheap, but worth it if they work. We have had our PRAA pup on the High Energy GI diet canned food from Royal Canin and I think it works well with the calories needed and doesn’t sit in the stomach risking regurg, plus it is easy to make into a slurry.

When you add ANYTHING to dog food, you are altering the nutritional composition. A young puppy needs specifically what is in dog food, proper amounts of protein, calcium, etc. When you add anything you are increasing some, decreasing others, some may not change But it is no longer a balanced diet.