A critical review of the value of genetic distance studies in conservation of animal genetic resources

There has been a veritable explosion of projects in recent years aiming to calculate genetic distances between domesticated breeds of animals and the number of such projects is still increasing. The extent of this can be appreciated by a glance at the recent proceedings of the 26th International Conference on Animal Genetics (ISAG 1998). All domesticated species are being targeted, using breeds from both developed and developing countries and projects are now almost exclusively based on microsatellite marker loci. Although the goal in a few cases is to provide insights into the history of animal domestication (see, for example, M ac H ugh et al. 1997; L au et al. 1998), the most common justification for genetic distancing projects is their importance for helping the decision-makers to identify genetically unique breeds so that they may be prioritized for breed conservation purposes (e.g. H all and B radley 1995; M oazami -G uodarzi et al. 1997; C rawford and L ittlejohn 1998). On a world-wide basis there are roughly 3000 breeds and breed varieties of the seven major mammalian species – cattle, pig, sheep, goat, horse, donkey and buffalo (FAO 1995). Of those with population data, 23% are either endangered or critical (FAO 1995). In addition, in the current century it is estimated that at least 600 breeds have been lost (H all and R uane 1993). On the poultry side, the picture is even worse as over half the breeds of the five major species (chicken, domestic duck, muscovy duck, goose and turkey) are thought to be endangered or critical (FAO 1995). At the same time, there is often a lack of even the most rudimentary information on many of these breeds. Basic phenotypic data, including approximate figures for population sizes, are currently available on only 50% of the world’s animal genetic resources (AGR) (H ammond 1998). There is therefore an urgent need to act now to prevent the rapid erosion of AGR. This is especially true for breeds in developing countries, where many will be lost without ever having been adequately characterized or studied (K& ouml ; hler -R ollefson 1997). However, resources (both in terms of available manpower and finances) are limited in this area and appropriate use of these resources is therefore of vital importance. Given the large amount of current activity in the area of genetic distancing of domestic breeds, the aim of this article is to critically examine the value that genetic distance projects have for breed conservation.