Opposite for me, at least with the one cat. She had some allergy to one or both of two other brands. Tried Purina cat chow naturals (because sale) and she showed small but noticeable improvement. Continued with it and full recovery (lack of better word). I have no intention to change her feed again, even among the Purina line.This is totally my opinion and what I have personally experienced first hand with Purina products so do with this information what you will.
My dog was on multiple Purina feeds. Different lines, Pro Plan, etc. We tried every Purina dog food line they offered per my vet saying it is really great food. She would puke 1-2 times a week. Some days she wouldn't eat all and go two days without eating. Her coat was dull and she just did not want anything to do with the food. She would consistently puke/dry heave one to two times a week on Purina. Finally stopped listening to the vet and switched her to Farmina dog food. She scarfs her food down and has not thrown up one time or had any other gut issues. She begs for more food and waits for her bowl to get filled now and I could hardly ever get her to eat any of the Purina food.
My cats were also on different Purina cat food lines during this period. I have three cats. All of them had runny/diarrhea poop, always. I also found mold in two different bags of cat food. I reported it and they sent me coupons for more Purina food in the mail. I switched them to Wellness Complete. They have had solid completely normal poop since.
My horses were on Purina grain. I actually had blood work pulled on her because her coat was soooo dry and dull I thought she was having other issues. Like her hair literally looked fried and was bristly to touch. Absolutely no shine to her and she just looked like absolute crap. She also was taking forever to shed out in the spring. Switched her to Buckeye and her hair has been bright, shiny, and sheds out fantastic in the spring since. Not to mention, the amount of feed required a day for Purina grain is insane. You have to feed 8-11 pounds a day of their feed and it is not cheap either.
So in conclusion, I don't think Purina products are all that in my opinion. Don't get me wrong, some peoples animals do fine on Purina products which is great for them but in my experience with ALL my animals which are different species, I have not been impressed with the results. It would not surprise me if their chicken feed is also poor quality. I have not done much research about Purina in general and who they are associated with and where they get their resources from but in my opinion, their quality of feeds does not match the price tag nor do I care for the results.