I have always been asking myself this question for a while now.
I have a 2 year old AQHA, who is EXTREMELY calm. She has the attitude of a 'been there done that' horse. She's always quiet, stands, sometimes she will almost fall asleep.
However she yawns a lot. I know some horses when under stress will yawn a lot. Kinda the same way with dogs. But my horse just doesn't show sign of stress, pain, etc.
She's always been the, I'd rather be asleep kind of horse. Even in the pasture. She doesn't even play, when the other horses want to she gets upset, kicks them in the face and walks away and go eat some grass. Even when the horse is literally up her butt trying to get her to play.
From what I have been told, horses don't yawn because they are tired, etc. They will yawn because stress, pain, etc. But I still don't see any of those signs.
When I put the bit in, for flexing on the ground (btw- I use a myler level 1 dee ring), she will yawn. I haven't seen any sores in her mouth and the vet said her teeth were fine. When I go to flex her from the ground she rolls her eyes to the back of her head. Doesn't gap the mouth, and gives to the pressure. But she will do it.
Any tips? Suggestions?