It became obvious that AI was the primary way of finding out which bulls were red carriers. Prior to AI, few red-carrier sires were uncovered because their service was limited to one or a few herds. Such herds often had no carrier females, and there was only a 25% chance that a carrier bull mated to a carrier female would produce a red calf. If a red and white calf were dropped, it was often concealed and quietly removed from the herd.