Cryopreservation of boar semen and its future importance to the industry.

Whereas AI has arguably been the most important management tool leading to improved herd productivity, long-term storage of semen brings forth additional advantages to producers of agriculturally important animals and the AI industry. Semen cryopreservation greatly facilitates the distribution of agriculturally desirable genes, rapidly increasing herd productivity. Of particular importance to the pig industry, the use of frozen semen would help to control transmission of certain pathogens, thereby protecting the health status of the herd. Moreover, a reserve of cryopreserved semen would minimize the effects of a sudden outbreak of a contagious illness or a natural disaster. Successful cryopreservation of boar semen is necessary for international sales. Finally, effective gene banking depends on the availability of functional, cryopreserved germplasm. Despite these potential advantages of long-term semen storage, porcine sperm are notoriously sensitive to cold temperatures, and frozen-thawed semen is not routinely used by the industry. The objective of our laboratories is to develop protocols for efficient long-term storage of porcine semen using cryopreservation. We hypothesize that since the sperm plasma membrane is the primary site of cold-induced damage, reinforcing the membranes with molecules having particular properties, such as cholesterol, will improve the ability of boar sperm to withstand cold temperatures and cryopreservation protocols. Based on our data, such approaches should help alleviate the problems with sperm function after cooling, thereby resulting in better survival and motility characteristics, and reduced non-regulated capacitation and spontaneous acrosome reactions.

Antioxidant status of the lower oviduct in the chicken varies with age and dietary vitamin E supplementation.

Protection of sperm membranes against lipid peroxidation is a pre-requisite to prolonged sperm storage, both in vivo and in vitro. As females from avian species can store spermatozoa in the utero-vaginal junction (UVJ) for prolonged periods, we investigated the mechanisms involved in antioxidative protection of the plasma membrane of chicken sperm in this region. Comparisons of concentrations in nonenzymatic (alpha-tocopherol, ascorbic acid, and GSH) and enzymatic (GSH-Px, SOD) antioxidants among the vagina, UVJ and uterus of sexually mature chicken hens revealed tissue-specific profiles, with higher ascorbic acid content and increased GSH-Px and SOD activity in the UVJ compared to other regions of the lower oviduct (vagina, uterus). Deterioration of the antioxidant profile in the UVJ was observed in aging hens, but it was partially compensated by dietary supplementation with vitamin E (130 ppm). It is concluded that the chicken UVJ provides a complex defense barrier against lipid peroxidation of the sperm membrane during in vivo storage, which can be partially improved by dietary supplementation with vitamin E. The protective effects of this barrier decline over time during the reproductive season.

Roles of antioxidants on prolonged storage of avian spermatozoa in vivo and in vitro.

This review focuses on natural and assisted prevention against lipid peroxidation in avian spermatozoa. The presence of high levels of n-6 polyunsaturated fatty acids (PUFAs) in the plasma membrane creates favorable conditions for the formation of peroxidative products, a major cause of membrane damage which may ultimately impair male fertility. However, a complex antioxidant system involving vitamin C, vitamin E and GSH is naturally present in avian semen. Coupled with a battery of enzymatic defenses (e.g., SOD, GSH-Px either Se- or non-Se-dependent), this system acts to prevent or restrict the formation and propagation of peroxides. The presence of specialized sites dedicated to prolonged sperm storage in avian females raises the question of durable protection of sperm membranes against peroxidation. Preliminary observations have revealed the presence of a specific antioxidant system at these sites in which vitamin C could exert a major role. From a practical standpoint, the extensive use of artificial insemination in poultry, along with the emergence in some species of workable techniques to cryopreserve spermatozoa, demand better control of peroxidation occurring in the plasma membrane of spermatozoa before or during storage. Dietary supplementation with vitamin E is effective in limiting lipid peroxidation of sperm plasma membranes, both in chickens and turkeys. In addition, organic Se with or without vitamin E stimulates Se-GSH-Px activity in seminal plasma. Preliminary observations in female chickens have also revealed the effectiveness of dietary supplementation with vitamin E, organic selenium or both to sustain fertility in aging flocks.