BackgroundIn 1946 there were 300 breeders of poultry in Canada. Today, 90% of the broiler chickens in North America and 90% of layers worldwide come from 2 breeder companies each; none of these companies is Canadian owned. Many genetic lines at institutions and research facilities across the country have also been dropped. According to a 2005 survey of institutions at Agriculture and Agri-Food Canada (AAFC) and the Faculties of Agriculture and Veterinary Medicine, only 5 institutions still carry genetic stocks, representing 33 lines of chickens in 23 different populations. These stocks of live birds are at continual risk from disease and budget cuts. There needs to be an economical way to address this drastic reduction in the genetic diversity of poultry stocks in Canada.
Freezing and storing semen, as has been used to preserve genetic stocks in other agricultural species, does not work well with poultry. Furthermore, the large size and fragility of the avian egg prevents any attempts to freeze its genetic material. Although freezing and storing cells from undifferentiated embryos has met with some success, the procedure to reconstitute flocks is technically difficult. Dr. Silversides and his team suggest an alternative procedure. They have demonstrated that ovarian tissue can be collected from day-old chicks and transferred to recipient chicks. They have also shown that testicular tissue can be transplanted from one chick to another resulting in live offspring once the recipient reaches sexual maturity. The implication of these results is that these tissues can be collected from chicks of genetic interest and frozen for long-term storage. When there is a need to regenerate flocks, the tissues can then be thawed and transplanted to recipient chicks that, upon reaching sexual maturity, can be bred to produce offspring with the genetic makeup of the transplanted tissue.
Research ProgressThe aim of this project was to freeze the gonads of 120 individuals from each population of chickens currently kept at AAFC and university facilities across Canada, with the eventual goal of recuperating offspring from each flock. Thus far, tissues from 1558 individuals representing 18 populations from 3 institutions were frozen. Unfortunately, due to hatching problems, enough material was collected from only 3 populations (there needs to be a certain number of individuals recuperated per line to produce enough birds in a flock to avoid inbreeding problems). Attempts have not been made to regenerate flocks from any of these frozen tissues.
Future WorkDr. Silversides and his team will continue to freeze gonadal tissue from lines of birds across the country. Although the proof of concept of recuperating flocks from frozen gonads has been established, Dr. Silversides notes that long-term institutional commitment is required to form a fully functional gene bank.
Funding$69,000 (CPRC $34,500, AAFC $34,500)
PublicationsSilversides, F. G., Shaver, D. McQ. and Song, Y. 2007. Pure line laying chickens at the Agassiz Research Centre. Animal Genetic Resources Information 40: 79-85.
Song, Y. and Silversides, F. G. 2006. The technique of orthotopic ovarian transplantation in the chicken. Poult. Sci. 85: 1104-1106.
Song, Y. and Silversides, F. G. 2007. Offspring derived from orthotopic ovarian transplants in chickens. Poult. Sci. 86: 107-111.
Song, Y. and Silversides, F. G. 2007. Heterotopic transplantation of testes in newly hatched chickens and subsequent production of offspring via intramagnal insemination. Biol. Reprod. 76: 598-603.
Song, Y. and Silversides, F. G. 2007. Production of offspring from cryopreserved chicken testicular tissue. Poult. Sci. 86: 1390-1396.
Silversides, F. G., Song, Y., Renema, R., Rathgeber, B. M. and Classen, H. L. 2008. Cryopreservation of germplasm from chickens kept in Canadian research institutions. Can. J. Anim. Sci. 88: 577-580.