The Challenge

Today’s commercial poultry are generally sourced from only two breeders. This means that commercial avian genetics are becoming narrower and genetic variation is being lost. It is important to preserve genetic material so that we retain the ability to be able to breed birds and adapt them for potential new environments, disease resistance etc.

A common method of preserving genetic variation is to take genetic material (e.g. sperm) from living birds and freeze it for future use. However, avian genetic material it is difficult to store by accepted methods.

As an alternative method of preserving avian genetic material, Drs. Yonghong Song and Fred Silversides at Agriculture and Agri-Food Canada, have been working on transplanting ovarian or testicular tissue to recipient chicks. Pilot work had suggested that transplantation of ovarian tissue in newly hatched chicks can be successful.

The Research

To test their theory, ovaries were removed from day-old White Leghorn chicks and replaced with ovarian tissue from Barred Plymouth Rocks (BPR). Some chicks were administered an immonosuppresant, and all birds were raised to sexual maturity. The hens that received the ovarian transplants were inseminated with semen from BPR roosters (if the transplant was successful, this would result in black chicks). Black chicks were indeed produced – the first report of success using this technique.

In males, testes were removed and donor tissue was placed into the abdominal cavity or under the skin of the back or abdomen. Frozen/thawed tissue was also used for some of these transplants. All successful recipients of testicular tissue showed normal comb and wattle development. Once the birds were sexually mature, transplanted testes were removed from the hosts, cut into small pieces, and the fluid that seeped from the surface was collected. This fluid was used to inseminate BPR hens by surgically placing it in the oviduct. This procedure produced fertile eggs resulting in black, donor-derived chicks.

A simple freezing protocol was also used to preserve testicular tissue from day-old BPR chicks. This was later transplanted into the abdominal cavities of nine castrated WL chicks. This research established surgical techniques for transplantation of ovarian and testicular tissue in newly hatched chickens.

When BPR ovaries were transplanted into WL chicks, either fresh or frozen, the tissue attached and underwent development. When manipulated birds grew to sexual maturity, three of the nine birds in the immunosuppressed group and three of the 12 hens in the non-immunosuppressed group produced black offspring. Although ovarian transplantation in chickens has been attempted, this is the first report of success.

When recipients of testicular tissue were ten months of age, the researchers saw growth of transplanted testicular tissue in all three locations. If the hosts were completely castrated, testicular fluid containing motile sperm was easily collected from the transplanted tissue. Surgical insemination of this fluid directly into hens’ oviducts produced fertile eggs resulting in black, donor-derived chicks.

A simple freezing protocol was used to preserve testicular tissue from day-old BPR chicks, and after thawing, this tissue was transplanted into the abdominal cavity of nine castrated WL chicks. After 11 months, the recipients were sacrificed and fluid from the transplanted testes was collected. Surgical insemination of sperm collected from one transplant produced a total of 23 donor-derived offspring.

In the present study, chicken gonads were transplanted within 24 h of hatching. The successful production of offspring from transplanted tissue suggests that there is a window just after hatch that allows grafting in chickens. This finding is significant for transplantation in avian species because there is no avian immunodeficient animal model as there is in mice.

The successful production of offspring from cryopreserved chicken testicular tissue demonstrated that germ cells in tissue from newly hatched chicks can be easily frozen, and that spermatogenesis in the frozen-thawed transplanted tissue is maintained. Given that the morphology of the testes and the development of spermatogenesis are essentially similar in most avian species, it is expected that newly hatched testicular tissue of most or all avian species can be preserved in liquid nitrogen and subsequently used to generate mature sperm when transplanted into appropriate hosts.

The Bottom Line

Ovarian and testicular tissue was successfully transplanted between newly hatched chicks, and gonadal tissue was frozen using a simple protocol. Cryopreservation and transplantation of testes and ovaries provides a simple approach for the conservation of chicken germplasm and may provide a universal protocol for the conservation of avian germplasm of all species and lines.

April 2008