Thank you. Great points. It is not about how we do it in different ways. It is the question about what do you want from the animals. I dont think an end of session is negative for the animal. As long as the animal is reinforced for what we want from them.
With the horses, I always say stop putting food on the ground as end of session. The reason is you have to go from a little hand full to 2 hand fulls and so on. We always try to teach the animals that it is oke that we go and that we maybe come back. We also give the animals including the gorillas the chance to practise a behaviour we like to see after we end the session by adding enrichment at the right time, opening gates at the right time and adding reinforcers in the right position after the end of session signal is give.
Maybe this article helps: https://zoospensefull.com/2019/12/23/is-an-end-of-session-signal-effective/