The Fertility of Frozen Boar Sperm When used for Artificial Insemination

Cryopreserved mammalian semen is generally acknowledged to have an impaired fertility by comparison with fresh semen. The reduction arises from both a lower viability post-thaw and sublethal dysfunction in a proportion of the surviving subpopulation. The reasons for the loss of fertility are various. In this paper, factors affecting the proportion of survivors (e.g., cold shock susceptibility, cooling rate, diluent composition and osmotic stress) and factors influencing functional status of survivors (e.g., membrane stability, oxidative damage, membrane receptor integrity, nuclear structure) are briefly reviewed. The possible effects of cryopreservation on the role of spermatozoa in the early stages of embryogenesis are considered. In the light of this review, indications for new approaches for improving the performance of cryopreserved semen are offered.

The problems, aspects and methods of liquid storage and freeze-thawing of boar semen are discussed and a review is given on examination of spermatozoa by the recent fluorescent staining methods.

The prediction of sperm fertilizing ability has great economic importance for breeding herds when artificial insemination is used. Classical methods of semen evaluation generally measure the sperm concentration, progressive motility, percentage of viable cells, and acrosome morphology. These assays are poor in predicting sperm fertility, because only the samples with markedly poor quality can be detected. The development of new sperm tests that measure certain sperm functions is an attempt to solve this problem. On the other hand, the binding and penetration of the zona pellucida is one of the most important barriers the spermatozoa must overcome in the fertilization process. Also, the interaction with the oocyte plasma membrane appears to explain much of the variability in sperm fertilizing potential among fertile boars. Thus, the study of the relationship between sperm factors and in vitro fertility may be a good strategy and assays that include a study of gamete interaction may lead to a better way to predict male fertility than the routine laboratory evaluation of semen. This review will discuss the relationships between sperm factors and fertility in vitro and in vivo (AI trial) with both diluted and frozen-thawed semen. We will also try to analyze the problems and limitations related to the interpretation of boar sperm tests.