BILL– I’m going to fall back on the “That depends” answer here. Without any clear-cut guidelines (unlike the blood on the horse rule), how it is treated depends on the judge’s perception of what all is going on in the horse. There are a few judges (a minority) who will punish the first sound of grinding fairly severely. The majority will look at it in the overall context of the horse’s countenance and how he is behaving. This would apply to tail swishing as well. If his mouth is not gaping, if he doesn’t look rigid or locked, if it doesn’t appear to stem from problems with the rider’s hands, then it usually won’t hurt you too badly. Eric Lette, when he was chairman of the FEI Dressage Committee, spoke of “happy grinding” where other than the noise it made, it seemed to imply no other resistances. He pointed to some horses who ground their teeth when peacefully standing in their own stall. He felt it was unreasonable to punish a horse for a harmless habit.
On the other hand if the grinding goes along with other signs of distress, it will hurt your score in the collectives and sometimes in the individual movements as well.
Another factor which plays in occasionally is if the judge has had prior personal experience with a horse that grinds his teeth. This is a real wildcard! One judge may be a little more sympathetic and will overlook some grinding if she feels that it’s not your fault and you can’t do much about it. Another judge may say to herself, “I used to get killed for it. Others must suffer the same fate that I did!”
One rider I know was complaining that her horse’s grinding was distracting her.
“Try earplugs,” I suggested it.
“How will that make her stop grinding?” she wanted to know.
“It won’t,” I explained, “but if you put them in your own ears, you won’t hear her.”