horse moves jaw side to side with mouth open....?

[yas]

after a feed my horse will often 'yawn' and move her jaw side to side. Does anyone know why she might do this?

 

[spartcas]

Prolly her jaw is sore do you use a harsh bit? and if not I would have a vet look at it.

 

[Dustcover]

When did you last have the dentist to her?