Really I do not think you can, hair and bone is supposed to be, but I have a Dr. Who / Ali heifer that's all hair and bone no TH in her pedigree.
Now if you ask AJ all the steers winning are, so I guess if you go stand by the back drop every calf that gets it picture is. So if the calf looks like a winner it must be a TH carrier, at least that is what AJ says.