Hello, I am so sorry to hear about your pup.
Did you slowly reintroduce his puppy food, mixing in a little more of the puppy food and a little less of the chicken and rice at each meal? Or did you just start feeding him the puppy food again?
It sounds like your little guy has a very sensitive stomach. It may be that an abrupt diet switch was enough to cause massive intestinal irritation.It may also be that he has a food allergy too, and something in that puppy food is leading to gastrointestinal irritation.
I would look for a puppy food that is chicken and rice based and do a very gradual diet change over to the new puppy food.I like Purina Pro Plan chicken and rice puppy.If his previous food had wheat in it then Purina One chicken and rice puppy is another good food.
It should take a good week to properly switch from one food to another, very slowly adding more new food, less chicken and rice.
Please let me know if you have any further questions.
If you find that even with a gradual diet change he still gets diarrhea you may need to feed a true hypoallergenic diet.
Can I answer anything else?
I switched formats as I wasn't sure that you could see my responses.
Thanks for the reply, I agree that he has a very sensitive stomach and likely a true food allergy.
There are many different types of Purina. The ones that I recommended, Pro Plan chicken and rice and Purina One chicken and rice are chicken and rice based, although both also have corn. If you fed the regular Purina Puppy Chow it is very high in corn and that may be the allergen for him that is leading to diarrhea. Vet essentials also contains corn.
Nature's recipe makes a puppy food with Lamb and Rice that may sit well with him as it has no corn.
If you want to make a homemade diet I highly recommend that you work with a veterinary nutritionist as it is not easy to formulate a diet, let alone a puppy food that will allow him to grow normally. Your veterinarian should be able to direct you.
If not here is a link to the University of Edinburgh's Veterinary nutrition consulting service: http://www.ed.ac.uk/schools-departments/vet/services/small-animals/vets/services/nutritionservice