I think you meant, the number of times a horse breathes in a certain amount of time.
no jphone
please think about this. is a shiur of TIME. how long someone slept.
it is not a frequency. it is a length of time.
it is not how many breaths a horse takes in a designated amount of time. it is how long it takes a horse to breath a designated number of breaths. the number of breaths is fixed (i dont recall the number).
the length of time has been decided differently in different shitas.
it is not a joke
the Torah frequently derives shiurim from naturally occurring events.
please ask a Rav if you still dont understand