**2.1 Sperm motility**

Motility is one of the most important features of a fertile spermatozoa. It was the first, and continues to be the most widely used indicator of sperm function. Sperm motility is an important attribute, because it is readily identifiable and reflects several structural, and functional competence, as well as essential aspects of spermatozoa metabolism. Sperm motility is expressed as the percentage of total motile or progressively motile spermatozoa. This parameter is usually assessed by the subjective visual examination under a phase contrast microscope at 37°C using low objectives (10 or 20x). Light microscopic evaluation

Methods of Assessment of Cryopreserved Semen 549

Fig. 1. Selected defects in sperm morphology (boar spermatozoa): a) normal sperm cells; b) looped tail; c) acrosome detachment; d) loss of acrosomal contents (back arrow), proximal cytoplasmatic droplet (arrowhead); e) proximal cytoplasmatic droplet; f) kinked midpiece;

g) looped tail (black arrow), coiled tail (arrowhead); h) thickened midpiece.

of motile spermatozoa does not require expensive equipment, is a simple and rapid method for assessment of sperm quality, however, it is a highly subjective and not reliable assay for the prediction of fertility (Peña Martínez, 2004).
