Advantages and limits in the implementation of a sperm cryobank for avian genetic resources

International audience

anglais. During the last twenty years, progress in the avian reproductive biotechnologies allowed the constitution of germ plasm cryobanks developed in national programs. These cryobanks are very important for the conservation and the management of genetic diversity. Since the characteristics of the avian egg make it impossible to cloning or freezing embryos in the current state of our knowledge, three main types of avian reproductive cells/tissues are stored in these cryobanks: semen, primordial germ cells (PGCs), and gonadal tissues. The success of semen cryopreservation constitutes a higher challenge in birds than in most mammals or fishes. Indeed, the avian frozen-thawed sperm must show very high quality after thawing in order to keep the fertilizing capacity during a long in vivo storage in the female sperm storage tubules (weeks to months depending on the species) in the female sperm storage tubules before reaching the fertilization site of fertilization. The very high sensitivity of avian sperm and/or female tract to deleterious effects of usual internal cryoprotectants such as glycerol seems also to be quite specific of birds. For all these reasons, and also because artificial insemination is not routinely employed in poultry (with the exception of turkeys), the progress in the constitution of semen collections for cryobanking has been more slowslower than in many other domestic species. As for all animal classes, the other limitation of the use of cryopreserved semen is the need of backcross for the reconstitution of lost breeds. Conversely, a major interest of bird semen cryobanking is that high numbers of sperm are available in one ejaculate by non-invasive methods (simple massage), and many ejaculates/male are available through non-invasive methods, allowing the constitution of very complete collections. PGCs cryopreservation and culture constitute a growing alternative approach, also used for transgenesis. However, it involves highly specific laboratory skills, is very expensive, invasive, and its efficiency stays far lower than semen methodology. The freezing and transfer of young chick gonads is another alternative method that encounters a certain efficiency, but faces specificities between breeds and needs high surgical and technical skills.Consequently, semen cryopreservation is and will stay the most available, less expensive and less invasive approach for avian reproductive cryobanking. We suggest the constitution of wide semen collections as basis of all bird reproductive cryobanks, and complementary addition of more focused restricted collections of PGCs or gonads, depending on the availability and characteristics of the breed/line to be stored.