[sethammons]

My first thought was, for sure, the foxes you mentioned. But on the note of no domestic animals avoid some examples of drooping ears, while I'm sure you could find supporting cases, that does not seem to be the norm for horses nor cats. And opposite that, elephants seem to have drooping ears. While the claim might be valid, it feels weak.

[goofingaround]

One factor that affects the horse is that humans use ear position to assess a horse's mental state. Most trainers teach riders to pay attention to whether a horse's ears are forward, pinned back, etc. Humans therefore may actively select horses with upright ears.

[k__]

Also, they aren't predators