Whoa, how big are the hay bales? LoL
And sometimes, there isn't a "reason" that tying up happens. When my guy tied up, I was riding him bareback at a walk. I got off, hosed him off and then tried to walk him away and he wouldn't move. He barely exerted any energy in the ride. He was a barrel horse so a walk around the arena was nothing to him.
But yes, horses that are prone to tying up, definitely need to be cooled out very well before putting them up.
"The greatest pleasure of a dog is that you may make a fool of yourself with
him and not only will he not scold you, but he will make a fool of himself too."