MEMBRANE-ALTERATIONS IN BULL SPERMATOZOA AFTER FREEZING AND THAWING AND AFTER IN-VITRO FERTILIZATION

Membrane alterations in bull spermatozoa after freezing and thawing an d after the process of in vitro capacitation and fertilization were st udied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Even if the majority of the spermatozoa exhibited in tact membranes after freezing and thawing (90%), one could distinguish between 3 types of membrane defects depending of the different struct ures involved. The first type showed loss of plasmalemma over the enti re acrosome. In the second category the anterior part of the outer acr osomal membrane exhibited a pronounced extension, but was covered by a partly intact plasmalemma. The last category consisted of spermatozoa with extensive vesiculation and disruption of plasmalemma and the out er acrosomal membrane. This type of defect could not easily be disting uished from a true acrosome reaction. The cumulus cells showed an acti ve phagocytosis of both intact and acrosome reacted spermatozoa.