Can horses eat barley straw?

Donks have a completely different digestive system, designed to manage things with the fibre content of straw, so I wouldn't base what a horse can have on that alone.
Was just saying about the rescue place, i did say the horses too

my cob actually ate the straw from the gate ways at field we used to be at, owner put tsraw in all the boggygate ways and by morning he had scoffed the lot and left his hay, this was years ago when he was ok on hay, god i was panicking like mad thinking he would colic!
 
newrider.com