a long time ago (about 16 years ago) I watched a large portion of an animated short film. Thinking about it now, I'm not sure it was suitable for an audience of 6-8 year olds. I still have some very vivid images and clearly remember that I didn't get to watch its end and for many years I've been eager to see it, but I wasn't able to come up with the correct Google keywords combination to find it. The following are the information I still remember about it.
It's an animated colored cartoon, not fancy 3D animation.
It's basically about horses that live in a heavenly place, surrounded with clouds and it appears to be some sort of floating island.
The horses are portrayed mostly with a Homosapien posture (standing up on two limbs).
The horses engage in daily-life activities, one horse is pictured practicing Blacksmithery.
Main plot idea: At some point one of the horses suddenly stops his activity and then he walks and appears to be asleep but with open and strangely colored eyes while other horses stop their activities and appear to be sad about him. The other horses avoid looking at him by covering their eyes with their hands. The horse continues walking until he reaches a pit in which he throws himself. The fall takes a long time during which the horse is morphing into strange shapes and then he reaches a pupal state and as he continues to fall he comes out as some kind of Batoidea then he exists from the bottom of the floating island where he flies in the heavenly space.
I'm 95% certain it didn't have any dialogue, apart from random sounds the horses made to express surprise or sadness.
I watched it some time between 1995 and 1997.
I hope I was able to provide enough information to make identification possible.
Update: After jlmcdonald's answer I watched the film again, I was very shocked. I think the whole thing (watching the film long time ago when I was young and then watching it again) was a very interesting experience. I was surprised how little I remembered about the graphics/colors (I had a totally different image in my head) and how some scenes were vividly engraved in my memory. I was also surprised to see that I, indeed, watched the whole film the first time I saw it, but for some reason I thought otherwise. It turned out they weren't actually horses, but at the age of 6-7 that was the best I could come up with.
I know SE isn't big on greetings and thanks but, seriously, thank you all.