Don Huston wrote "put him in a trailer and take a drive," as a potential help for impaction. Several cowboys I have talked with recently have brought up this method for helping with colic of undetermined source. They'd had some good luck with it, feeling the vibrations help shake things loose, and wouldn't hesitate to throw a horse in a trailer and take him for a "drive around the block" (on Arizona working ranches, those can be LONG blocks, and the roads are not pretty). Often their attitude is "get tough or die"" so I guess a trailer ride is a step up on that philosophy. And it doesn't cost much to try, if a trailer is available, and the old guy can do it.