Anyone notice how awkward he got off his horse he almost landed on his arse on the ground at one stage. Is there any scene in the film where he mounts his horse himself and not his stunt rider mounting the horse? That would be interesting to see.
shareTracy was not in the best of health at that point (age 54), as well as struggling with his weight throughout his adult life.
He did not generally like riding in films (the same was true of Gary Cooper, star of High Noon, in fact), but Tracy was a good horseman when younger - for many years he played polo in Hollywood quite successfully, where the game was popular. He gave it up after the death of an acquaintance who was playing in a game.