Synaptic anomalies in fetal bovine oocytes.

Chromosome pairing abnormalities in oocytes of bovine fetuses ranging in age from 81 to 130 days were studied using the surface-spread whole-mount technique. The synaptic abnormalities included partial or total asynapsis, nonhomologous pairing, and mid-pachytene degeneration with asynapsis constituting the most common category. Oocytes showing synaptic abnormalities were less frequent in younger fetuses and more abundant in fetuses older than 110 days. Histologic signs of oocyte degeneration, evident in all fetuses, were most striking in ovaries of fetuses older than 120 days. The temporal relationship of these events suggests that chromosome pairing anomalies may be associated with oocyte degeneration, although their exact role in precipitating oocyte atresia remains unclear. The presence of abnormal oocytes and follicles in the vicinity of the medullary cords seems to suggest that these germ cells may be exposed to deleterious substances from the degenerating rete cords and that the synaptic errors may be the meiotic manifestations of chromosome damages sustained by germ cells during the repeated oogonial divisions in an environment unconducive to mitosis and maturation of female germ cells.