Читать книгу Bovine Reproduction - Группа авторов - Страница 155

Detached heads, also termed free heads or loose heads, are commonly found in low numbers in semen samples collected during late winter and early spring, suggesting that their occurrence is due to senescence. In these cases, the sperm take up the eosin stain uniformly, indicating that they were dead before ejaculation. Detached heads, both normal and abnormal forms, are also found in variable numbers with other defects following an insult to spermatogenesis. Large numbers of detached normal heads may be seen in cases of sperm accumulation associated with a failure to void aging sperm in the urine. Detached heads may occasionally be encountered that stain alive, usually in the presence of a variety of other defects, indicating an insult to spermatogenesis that has affected the formation of the connection between the head and the midpiece. Detached heads are not a normal phenomenon. Although a few are acceptable they should always be included in the differential count. The one notable exception is when assessing the true proportion of knobbed acrosomes (KAs) in a sample. Dead sperm eventually lose the acrosome; therefore acrosomal anomalies will not be visible. Disregarding dead, detached heads in this case will give a more accurate proportion of KAs present in the spermiogram. (Editor's note: a normal detached or free head may be classified as a midpiece defect because it results from separation at the junction of the midpiece and head.)