My wife uses an IAE calf crush and does them at 4 weeks or when horns are showing and never any complaints.To be fair after looking on IAE website ours must be an old type, no hinged rear side doors and has a chain to keep the locking handle fastened down. Chain always dragging in the sh1t, if handle isn’t locked down calf lifts head up and the handle hits you in the face, this has happened to old chap and the vet who both were rather p1ssed off when it happened!