What, how, and how much to feed zoo animals is not just trial and error.
If this is a reacton to my post, I was talking about quantitiy of
food at the level of an indivudal animal. Which is how I interpreted
one of the questions of @animalszoos. Despite all research and
experience (which is basically preceded by trial and error), on the
level of the individual animals you are going to need to try things out
and observe, because every individual is different.
You are completely right about 'what, how and how much' to feed an
animal on species/subspecies/breed or sometimes population level.
The basics are known (as I already wrote), but zoos need to finetune
it to the individual animals. That's what I tried to explain.
I wasn't necessarily responding directly to your post, I just used your phrase. I was trying to make the point that the feeding of zoo animals is much more standardized and scientific than what was being portrayed in the impression I was getting from all the posts. Actually, you and I are in complete agreement.