The fact that most of the cattle breeds currently living on earth are endangered has been documented in a plethora of reports. In this context it is only a minor issue whether the loss of genetic identity of a breed is brought about by extinction in its strictest sense or by permanent upgrading with other more prominent breeds.
Bodo, Buvanendran and Hodges (1984) have defined three different degrees of endangerment with respect to the probability of a breed to survive as a unique population:
• Normal
This status implies that there is no danger of the population in question becoming extinct. It is capable of reproducing without concomitant loss of genes and there is no obvious reduction in population size which might endanger the breed.
• Endangered
Endangered species are acutely threatened by extinction because the effective population size has become so small that loss of genetic variability cannot be prevented. The unavoidable high degree of inbreeding in such small populations also adversely affects the vitality of animals fit for breeding and there is imminent danger of suffering severe losses either spontaneously or by direct intervention.
• Critical
This status is a direct consequence of endangerment and implies that the population or breed has become almost extinct.
The American Minor Breed Conservancy (AMBC) has suggested the following classification of breeds:
• Breeds to be monitored
These breeds are characterized either by a gradual reduction of registrations during the last 25 years, or by registrations numbering less than 5000 animals per year.
• Breeds with only a small number of animals for which less than 1000 animals are registered each year.
• Rare breeds for which less than 200 animals are registered each year.
It has become a matter of utmost importance that decisions to establish embryo banks and gene reserves will be made in due time. Only this will ensure to a certain degree that enough cows will be available for embryo collection. To simplify matters we will assume that in most cases at least 1000 cows should be available (See Chapter 5.3). The population size of most of the breeds that are regarded as being endangered or critical nowadays is less than 1000. In these cases one should try to conserve at least the genetic potential that is currently available. One must take into consideration, however, that later reactivation will suffer from problems arising from insufficient numbers of stored embryos.
The establishment of genome and gene reserves is associated with considerable costs. This means that it will not be possible in the near future, due to financial and organizational reasons, to conserve all breeds that are threatened by extinction.
When evaluating losses of certain breeds one must take into consideration the fact that a number of currently available unique breeds threatened by extinction are probably closely related to other threatened breeds. In extreme cases the differences between such breeds may only be caused by the presence of a single or a few number of qualitative traits. It would seem justified to postpone conservation of such breeds and to introduce the genetic potential of these breeds into the gene pool of established breeds by controlled matings. Eventually this would ensure limited amounts of funds to be directed towards conservation of those breeds which appear most worthy of being preserved due to their respective individual domestication and breeding histories.
Conservation of cells, nuclei, oocytes, chromosomes, or individual genes should not be the only approaches towards conservation of the genomes of cattle breeds. At the present state of knowledge the chances of reactivating a breed from these materials would be too low. The significance of these conservation techniques lies in the supplementation of programmes designed to reactivate embryo and semen banks and in the possibility to reactivate one or a few genes that might be required in the future. These additional gene reserves have the additional advantage of providing required material rather cost-effectively. In view of organizational, technical and financial considerations it would be relatively unproblematic to collect and cryoconserve tissue specimens at death from members of endangered species. The more involved techniques such as preparation of the tissues to establish, for example, gene libraries could be postponed until the material would be required. Under these circumstances it should not be difficult to raise the funds required.
The most obvious way to conserve an endangered cattle breed would be an attempt to prevent further reductions of the current population size. By intensifying breeding and/or providing sufficient organizational and financial help one could also try either to guarantee current levels or even to increase the population size. Since most of the endangered breeds are threatened by considerations related to economic management retaining sufficient livestock will be problematic. An alternative would be to keep such breeds in the form of farm animal zoos or by contracted farmers, although this would lead rapidly to problems due to unavoidable inbreeding over several generations and to genetic drift (See Section 4). In addition small populations suffer from the risk, which should not be underestimated, of occurring of widespread disease, accidents, or other unforeseen instances which might suddenly decimate a large number of animals or even the entire population.
The German Society for Breeding Research has published criteria which may be helpful in reaching decisions about the worthiness of breeds to be preserved.
Biological prerequisites
the population is genetically unique, i.e. crosses with cattle from unrelated breeds have not taken place;
there is no way of obtaining sires from other sufficiently large populations of genetically related breeds which are not endangered;
the effective population size has fallen below the minimum sizes required.
Genetic and economic considerations
The endangered breed differs from predominant breeds in several respects:
presence of traits which are of economic importance;
presence of traits which may become important but which are, as yet of no economic importance;
high frequency of major genes of potential economic importance
heterosis expectancy
Cultural and ecological considerations
particular regional significance of the breed in question
advantages in view of environmental care or ecological equilibria
recreational value
particular rare characteristics with respect to form, colour, or behaviour.
Efficient reactivation of genome reserves can eventually be achieved by collection and storage of embryos, preferably in conjunction with storage of semen.
Risks may be minimized by taking care that not all embryos are stored in a single bank at a single location and it would be advisable to set up suitable banks in at least three different locations. We therefore suggest that one third of the embryos should be stored in:
embryo transfer or artificial insemination stations of the country in which the endangered breed predominates or predominated, and in which collection of embryos has been carried out;
stations of each continent. Such stations should be established as central embryo banks specializing in the establishment of gene reserves. These banks should also store an appropriate fraction of all embryos collected within this continent;
specially established central embryo banks which store conserved material obtained world-wide and which organize collection and also provide material for reactivation.
Allocation of gene and genome reserves to different banks will be the only way to safeguard against and to minimize losses incurred for example by accidents, war, power failures, or ideological reorientation. Stored semen should be treated in the same way as stored embryos.
For other material such as cells, tissues etc. that can also be stored, storage in continental or central institutions would be sufficient. This approach would be appropriate especially in view of the fact that further processing of the stored material requires great technical expertise and is labour-intensive. At present this potential has been realized in only a few countries.
The following strategies are suggested for ex situ cryoconservation of endangered cattle breeds:
Registration of existing cattle breeds;
Grading of breeds according to the degree of endangerment, numbers and degree of relationship of available animals;
Grading of breeds according to worthiness for conservation;
Calculation of costs required for establishing and maintaining central institutions and for conserving individual breeds;
Funding and establishment of organizations and institutions responsible for collection and storage of genetic resources;
Establishment of cryoconservation banks for storage of embryos, semen, and tissues;
Documentation, characterization, and publication of data related to conserved genomes and genes;
Formulation of prerequisites essential for partial (genes) or complete (genomes) reactivation of a cattle breed.
