Diadem/crater defects in spermatozoa from two related angus bulls

The diadem/crater defect was studied over several months in two related 20‐month‐old Angus bulls. In bull 1, diadem/crater defects were present in 2–99% of ejaculated spermatozoa at various times during the evaluation period. In bull 2, affected cells varied from 20% to 94%, with other abnormalities (head and acrosome defects, coiled tails, proximal cytoplasmic droplets) also common. Single sire mating trials conducted over 26 days during an apparent recovery phase showed normal fertility (approximately 50% pregnancies per estrus exposed). Both resting and gonadotropin‐releasing hormone (GnRH)‐stimulated testosterone values were within nor‐mal limits. Histopathological evaluation of testes showed no obvious hypoplastic, inflammatory, or degenerative condition. Electron microscopy of ejaculated spermatozoa demonstrated the characteristic diadem pattern of craters in the equatorial region of the head. Many cells from bull 2 contained large craters in other regions of the nucleus. Electron microscopy of testicular tissue demonstrated nuclear invaginations lined by a single unit membrane in round spermatids. Lesions in elongated spermatids were more pronounced, with curling of the nucleus and large membrane‐filled cavities in the chromatin occurring in addition to craters in the equatorial region of the nucleus