[papsosouid]

You vastly overestimate the quality control, safety testing, and labelling requirements of pet foods. Pet food does not need to be certified, or pass any tests to be sold. Pet food is labelled according to AAFCO guidelines, which merely specifies how much protein/fat/calcium/phosphorous and a few other things are required. That's it. Those pet foods for fat dogs and old dogs and young dogs and kidney health and shiney coat and furballs and clean teeth are just ordinary pet food. They do not need to be different in any way. The manufacturer can literally put the exact same food into all of those bags, and none of the claims on them need to be verifiable.

>Talk to British people about dog excrement, and there are people of a certain age who remember dog poo being white and furry

That is because they remember dogs eating meat. Now dogs eat corn. There is no patent on dog food that makes white poop.

>Notice, also, that pet food is often a mix of biscuits and meat, or just meat, or just biscuits

This is for the benefit of marketing the product to people, it has nothing to do with nutrition.