Prognostic value of spermatological parameters as predictors of in vitro fertility of frozen-thawed bull semen.

Cryopreservation imposes irreversible damage to sperm membranes, such as swelling and disruption of plasma and acrosome membranes, changes in membrane fluidity, altered influx of calcium, and changes in enzyme activity. Morphological integrity of the sperm plasma membrane has been widely studied using different techniques, including exposure of spermatozoa to hypoosmotic solutions (provides information concerning the biochemical activity of the sperm tail membrane), supravital test using eosin stain (yields information regarding sperm head membrane integrity), and Trypan-blue Giemsa stain (TBG; reveals both sperm plasma membrane and acrosome integrity). The objective of this study was to combine these tests in order to provide information about the integrity of the whole sperm surface, as well as acrosome status, and determine if the results of these tests were associated with sperm in vitro fertilizing ability. Stepwise regression analyses yielded a model in which fertility (maintain variable) was expressed as a combination of the results of different spermatological parameters (independent variables). The results of a test combining supravital eosin staining of samples previously submitted to hypoosmotic swelling test (STHOS) accounted for the greatest proportion of variation in fertilization rates (78%). Inclusion of the results of dual staining with TBG increased the proportion of variation in fertility rate that could be accounted for to 82%. Therefore, sperm plasma membrane integrity and function, and acrosome integrity can be considered important variables for normal sperm function and STHOST and TBG could be used for the prognosis of the potential fertility of bovine semen samples used for IVF or AI.