Most of the genetically transmitted lethal traits cause death of the calves prior to or shortly after birth. Numerous cases of such abnormalities are on record. Most of the lethal traits are recessive and may remain hidden for many generations. The removal of lethal genes requires test matings and rigid selection. Ideally, purebred animals should be free of both undesirable and lethal genes. This is possible only by eliminating those sires and dams that carry the undesirable recessive character. In addition, producers must DNA test both phenotypically abnormal and normal offspring produced by these sires and dams because approximately half of the normal animals carry the undesirable character in the recessive condition.

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