A large proportion of the 500 different breeds of cattle currently available world-wide is considered as being endangered. Because these breeds are of cultural, historical, and genetical importance attempts are being made to conserve genomes and individual genes by employing modern breeding techniques. This would allow, if required, the reactivation in their original form, of individual breeds that might have become extinct. Ex situ cryoconservation is considered to be the method of choice for long-term storage.
The conservation of genomes can be achieved either by storing semen, embryos, cells, nuclei, or oocytes. Establishment of gene or cDNA libraries would be an appropriate means of gene conservation. Cryoconservation of cells or tissues obtained from animals would be a rather cheap alternative. If it were carried out now this would allow the establishment of gene libraries to be screened for the desired gene(s) at later times. Full reactivation of breeds can only be achieved by means of conserving the entire genome. If individual genes or gene clusters are required in the future the conservation of cell material containing the nuclei would be entirely sufficient.
Reactivation of cryoconserved material requires the use of several biotechniques. As far as gene reserves are concerned this would comprise techniques for artificial insemination, embryo transfer and embryo manipulation. Individual genes that have been recovered from stored genomes could be reintroduced into cattle populations by employing molecular-biological and embryological techniques in close cooperation.
From a geneticist's point of view the establishment of genomic reserves in the form of embryo banks would be advantageous because storage would not be associated with loss of genes or alteration of gene frequencies, factors which are inevitable if small populations of livestock are kept. It is most important to establish several gene libraries or to conserve cells from different animals of an endangered breed to guarantee that a sufficient number of clones are available for representative libraries.
For practical purposes embryo banks can be established either by stationary embryo transfer stations or by mobile units. It will be important to split the collected material and to keep it in at least three different units allowing long-term storage.
Model calculations demonstrate that a population size of at least 1000 animals will be required in order to be able to reactivate from an embryo bank 25 calves fit for further breeding. This points to the fact that it is about time to prepare a comprehensive inventory of breeds currently available.
It is essential that financial means together with the organizational infrastructure are provided to allow the efficient establishment and maintenance of embryo banks for breeds that have been classified as endangered or those that should be retained.
