From what I was told by my trainer (who also judges) you CAN use one. HOWEVER you need a vet report that it's medically necessary. Actually I got one for my qh just in case (as she has head shaking syndrome). But the way I do it I have full mask on during warm-up and waiting, and take it off/put fly spray on just 5 mins before entering the ring. Usually it's enough for those 5-7 mins test takes.
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."