There have been other materials used for bedding horses, with some being new ideas and others reasonably old. I have seen flax, hemp, peat moss, and shredded bark.
I don’t have enough experience with any of these to comment here. The person using the flax bedding said she liked it. Hemp is not readily available. Peat moss has not been used in my practice but is not much different than dirt. Pine needles are used in the southern states but rarely.
When I saw shredded bark used, I was not impressed, especially when one of the shreds entered a new castration site and set up an infection.
There is no related material for this topic.