I am going to research that micro flora. The food waste is interesting but I don't see how that can be such a big deal when so much more food is consumed by ranging.
Happy hunting. Wish I had a few good articles to link you to but it's info I've found offline.
I think the food waste issue only relates to permanently caged birds, which was the industry's big beef about it.
The inherited and acquired intestinal fauna and flora prevent or resist many diseases and help digest food more efficiently, so you may find related info if you research the scientific details on why mammal infants don't live on cooked milk, or require probiotics etc added. Also saliva transmission of gastrointestinal fauna/flora etc.
Ok, this is gross, but did you know they (medical experts in the relevant field) do feces transplants? Like, for a human who can't digest food correctly because they're lacking the correct intestinal fauna/flora. They literally take poop from a healthy human and put it into the sick one. This colonizes (ha, a pun) the sick human's insufficient bowels with the necessary microorganisms to digest food correctly. Obviously NOT a popular treatment. But can be lifesaving. Also humans exchange/share their intestinal fauna and flora when they kiss or touch their mouth after touching another's hand, etc, all much the same as chickens, dogs, cats, etc providing their young with a decent population of digestive organisms.
Best wishes.