A sterilizing tail stump sperm defect in a Holstein-Friesian bull

A case of sterility in an 18-month-old bull of the Holstein-Friesian breed was investigated. A semen sample sent to the laboratory showed a very low sperm concentration and abnormal sperm morphology. On the preliminary examination, the major sperm defect (60-70%) seemed to be tailless heads. When higher manification was used it was found that most of the defective heads had a short tail rudiment, a tail stump 2-3 mu long. Loose sperm tails were seldom seen in the smears. The defect has been described previously from Canada where it has occurred in different breeds, including Holstein-Friesians. The dam of the Danish bull in question was inseminated with imported American semen, and the sire is one of the most demanded Holstein-Friesian bulls at present. The possible heredity of the defect is discussed.