The knobbed acrosome defect in beef bulls.

The knobbed acrosome defect was found at levels of 25 to 100 percent of spermatozoa from 16 of 2054 beef bulls. The incidence of this defect appeared to be particularly high in the Charolais breed. Pedigree analysis of some of the affected Charolais bulls indicated there may be a genetic predisposition for this sperm defect. In eosin-nigrosin stained semen smears the most common form of the abnormality was a flattened or indented apex of the sperm head. A refractile bead at the apex of the sperm head was seen less commonly. Electron microscopy of the spermatozoa from one bull showed that the abnormality was similar to the knobbed sperm defect previously described in Friesian bulls. A breeding trial confirmed that bulls producing spermatozoa with a high incidence of knobbed acrosomes are infertile.