The horse that is breathing a little faster than at rest is to be expected in
the middle of a race.  No so for panting, flaring sides heaving, etc.  These
are all signs of problems in oxygen or heat or both .  
So remember that the vet may not COUNT the respirations, but he/she is aware
of HOW the horse is breathing with an educated glance.
I was able to pick up on an early colic just because of heavy breathing I saw
on a mare at rest.  IT JUMPS OUT AT YOU.  
Just my .02
Becky Hackworth
Jam (slowly back at work) Gina ( finished Mt Laguna with only 2 B's out of 3
vet checks...her best ever)  and other assorted kids and critters
Alpine,CA