Ultrastructure of the tail stump sperm defect in the bull.

A characteristic major sperm defect, with about 60% of the sperm cells showing a rudimentary tail stump, was found in two sterile Danish bulls of imported origin. The condition seldom occurs, but seems to be widespread and has been observed in several breeds of cattle and in different animal species, including man. Electron microscopy of ejaculated sperm and testicular tissue from one of the bulls has shown that a dysfunction of the centriolar apparatus during spermiogenesis is likely to be the cause of the defect. In ejaculated defective sperm the proximal centriole is often found connected with the normally transitory organelle, the centriolar adjunct. In the defective spermids the distal centriole has lost the faculty to form axonemal fibers, so that no tail formation can take place.