Let's talk interactive exhibits...

[Aardwolf]

Bread for zoo animals back then was very different from the bread we have in stores today - much heartier, often with other ingredients baked into it, such as meat. Many zoos had their own bakeries for customizing diets for animals. It would be fair to say that the breads were an early attempt at making chow for different animals.

 

[JVM]

I think animals being fed actively toxic substances being brought in by visitors, as brought up by @Great Argus or being fed non-nutritous actual food as I mentioned, are both valid but distinct conversations.

I had intended to shed light on why in-zoo feeding animals became a discouraged practice, not argue against supervised feeding.