That's why most breeders have it in their contract to feed the same food until they're @ least 6 months old. If the puppy is 12-15 weeks old or bigger, about 2 #'s, it's less risky, but very dangerous for younger 8 week, under 2#'s pups. I also wonder why a breeder is feeding Purina in the 1st place.
Is this what the momma eats too? It's not a 'premium brand', not the BEST food for breeding bitches.
Switching food on a very young puppy is very risky.
1. it can cause additional stress, stress = bloody poop
2. it can cause stomach upset, tummy upset = diarrhea
3. diarrhea + bloody poop = dehydration
4. dehydration in a small puppy + they lose their appetite = hypoglycemia
5. hypoglycemia + they can go downhill very fast = trip to the ER or vet
Some dogs do not eat the old food when you transition them, they will pick out the new & leave the old. So in this case, it's cold turkey & hope that they don't get a stomach upset. Some dogs do fine w/cold turkey switches, some do not. When switching from a store brand to a premium brand, they recommend transitioning slowly for 7-10 days. Just be prepared to take on the responsibility of what can happen when the pup gets any loose stool or diarrhea when switching foods, take them to the vet asap.