What is the purpose of this?

Its a anti windsucking bit. The idea is that there wear it in the stable and if they try to crib the air goes through the holes.
 
Aparently they make a noise and scare the life out of the horse if they windsuck. Sort of a whistle noise, supposed to discourage them from doing it.

I have never seen one used so I am not sure if they work.
 
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