Donna
the mass market brands (Pedigree, Butchers, Chunky etc) have certain things in common:
1. meat sources are "animal by products and animal derivatives" - i.e. claws, guts, skin etc. My OH ran a pet food factory - I've seen this, although it arrives in huge frozen blocks....
2. lots of preservatives and flavourings.
The so-called "premium" brands, wet and dry, that people on here recommend (James Wellbeloved, Nutro, Burns, Arden Grange - all dry, and Nature Diet (wet)) use higher quality ingredients (meat rather than "derivatives"), fewer cereals - used to provide necessary complex carbohydrate balance and fibre content, rather than over-used as cheap bulking material and source of excess calories - and some vegetables for simple carbohydrates. All pet foods also have "min-vite supplements" - i.e. proprietary mineral- vitamin pre-mixes added to ensure that the foods we're talking about here are "complete" - i.e. all nutritional requirements for your pet are met by feeding just that food, no need to "mix and match".
I found with Paddy that, on Pedigree puppy pouches, he went loopy - really hyper - which I put down to the preservatives/additives. No such reactions on premium foods. I now feed a wet food called Forthglade - looks like NatureDiet and until last week, it looked to have settled his recurrent colitis down. Currently he's on an exclusion diet from the vet, and not sure what I'll be doing going forwards - may even try BARF or another raw diet....