The identification of Jon-Red as a carrier in January 1989 coincided with his removal from active service. Because of the extensive testing of U.S. bulls that has occurred over the past five years, we are confident that no carriers are among the top 400 TPI bulls as of July 1992. We expect that the incidence will decrease in the North American Holstein female population and any other population that uses U.S. Holstein semen extensively. A similar pattern has been seen in Europe. Such profiles, with relatively brief periods of intense testing activity, are to be expected for inherited disorders in animal species when an efficient testing program is instituted.
Testing permits identification of carriers and their removal from the breeding population.
This decrease in frequency of the condition reduces the need for further testing. The reappearance could occur by generation of a new mutation or by emergence of the same mutation from an untested carrier distantly related to a known carrier.