The horse that I am currently riding sometimes acts a little sore on her right front. It only happens when she is on hard ground (ex. Concrete, the barn driveway), and she is totally fine in the indoor arena (which has rubber footing). She has been completely checked out by the vet and farrier and they do not see anything wrong with her...
The only thing we can think of is that she is feeling the pain that her mother is having right now. Her mother has been lame on HER right front for a couple months now, (at first the prognosis was grim, but she is doing much better now).
I have heard of this in humans before, like with men experiencing morning sickness when their wives are pregnant, or twins feeling eachother's pain.
...But have you ever heard of horses feeling other horses' pain like this?