REVIEWS Conserving livestock breed biodiversity Stephen J.G. Hall and Daniel G. Bradley L ivestock breeds are recog- nized I as important com- ponents of world biodiver- sity because the genes and gene combinations they carry may be useful to agriculture in the future. The gains in economic efficiency, which may result from using this genetic material, could far out- weigh the costs of conserving the breeds in question 2. Many breeds, once economically important, are now very rare, and yet they pos- sess characteristics of potential value (Fig. 1). Growing awareness of the importance of conserving the biodlversity of livestock breeds is paralleled by genetic advances that will help objective planning of conservation. Inventories of breeds, long advocated, are now being established and concepts originally formulated for the quantification of species diversity are being applied. The breeds thus conserved will provide valuable resources for the future of agriculture, especially in the developing world. Breeds as the basis of live- stock genetic conservation A breed is 'a group of animals selected by man to have a uniform appearance that distin- guishes them from other members of the same species'3; worldwide, 3213 breeds of ass, cattle, goat, horse, pig, sheep and water buffalo have been enumerated 4, and possibly 1000 breeds altogether are at risk of extinction5. While, in principle, valuable livestock genes could be conserved by maintaining a large random mating pool without reference to breed, this is not favoured mainly because the genes would be difficult to evaluate and to retrieve 6. In addition, specific breeds may possess unique combinations of alleles as the result of adaptation to different environmental chal- lenges, which would be difficult to recreate. Livestock pos- sessing important quantitative traits resulting from such combinations will only be amenable to assessment and exploitation when managed as discrete breeding entities. Livestock genetic conservation measures are therefore likely to remain focused on the maintenance of breeds. The major threat to rare and minority breeds is absorption into numerically stronger breeds, usually by repeated use of males from the stronger breed 7. Accordingly, the basic prin- ciple of breed conservation is the promotion of pure breed- ing, which has traditionally been by the keeping of pedigree records. Threatened breeds can be protected by ex situ (cryogenic) or in situ methods, the former being preservation as semen or embryos, the latter, the protection of breeding stocks 6,8. Currently, no livestock breed is conserved purely cryogeni- cally, although for some breeds in situ programmes are backed up by semen banks. This is most evident in Europe, where, out of 877 rare and numerous breeds of cattle, sheep, goats, horses and pigs surveyed, 367 (mainly cattle) are sup- ported in this way9. In the rest of the world, semen or embryo banks exist for only six out of 126 endangered breeds for which data have been collated 5. Most of these banks are very limited in the numbers of individual animals that have contributed to them. Conserved breeding stocks may be special herds or flocks often under institutional ownership, like the Rambouillet Merino sheep in France or the Chillingham cattle in the UK6.9; alternatively they may comprise many separately owned breeding units under the aegis of a breed society. In the Stephen Hall is at the Dept of Clinical Veterinary Medicine, Madingley Road, Cambridge, UK CB30ES; Dan Bradley is at the Dept of Genetics, Lincoln Place Gate, Trinity College, Dublin 2, Ireland. developed world, much livestock diversity is currently conserved in these ways. Conservation biology and livestock biodlverslty In the future, it may be forbid- den to use cryogenicallyconserved material as today's conditions of collection may fail to meet future, more stringent veterinary stand- ards 8. Similarly, the preservation of livestock diversity as either naked or manipulated DNA sam- pies 10 has attracted support, but in the light of difficulties with trans- genic procedures G,it is now clear that initial expectations were over- stated and that this approach is of little use. However, because of the sophisticated tech- nology involved, ex situ procedures still continue to appeal to aid agencies. There is a danger that emphasis on such procedures will divert resources from projects based on in situ methods, through which not only the livestock, but also the traditional systems of which they are part, can be con- served. The primary challenge to conservation biologists is to facilitate the establishment of programmes that focus on live animals rather than uncritically to advocate the use of cryogenics. The maintenance of genetic variability by appropriate mating plans within populations under centralized control is well understood 6, but there is a lack of practical experience in most countries of the fostering of private ownership of threatened breeds and of their management with a view to genetic conservation. There has been little discussion in the literature even of such basic ideas of what is meant by genetic conservation as applied to livestock. For breeds that are administered by breed societies, the 'continuing rep- resentation in the pedigrees of current generations, of the largest possible proportion of those animals which were accepted as foundation stocks when records were begun TM might be an appropriate definition of genetic conservation. The animal resources of developing countries pose special challenges. Breeds are usually poorly characterized phenotypically. Furthermore, they will have to meet present as well as future needs and breed conservation programmes will have to be reconciled with breed development pro- grammes 12J3.The challenge is for such development to use indigenous, locally adapted strains rather than exotic imports, and in this context a practical paradigm for con- servation might be 'the rational use and protection of exist- ing local genotypes from genetic introgression '13 (Fig. 2). Many native breeds have great potential for increase of pro- duction, without loss of local adaptation, which could be realized by appropriate selection programmes. Highly sel- ected west European or north American livestock will only achieve their full productive potential under conditions of good nutrition and adequate veterinary care. Under rigor- ous local conditions, the native breeds are far more likely to be productive. TREE vol. 10, no. 7 July 1995 © 1995, Elsevier Science Ltd °)6 7