and by chance, homozygous for other unfavourable recessive ones. A second unrelated breed would be unlikely to be homozygous for the same undesirable genes. Thus a cross between the two would result in more vigorous offspring (Warwick, 1979). This ‘matching’ of breeds is not predictable. The total number of possible crosses is potentially infinite, and many un-tried crosses could produce valuable production stocks. The South American Criollo cattle whose numbers were in dramatic decline due to replacement by European and Zebu imports, have now been shown to have great potential in commercial crossing where the Criollo first crosses out-produce purebred imported and indigenous stocks. Populations should not therefore be discarded on the grounds of economic efficiency as measured at any one time, but should be considered with respect to biological efficiency operating within the context of a wide range of possible political and economic situations and a wide range of possible breed crosses (Henson, 1986).
3.1.2 Scientific Use Endangered populations should be conserved for their possible scientific use. This may include the use of conservation stocks as control populations, in order to monitor and identify advances and changes in the genetic makeup and production characteristics of selected stocks. They may include basic biological research into physiology, diet, reproduction or climatic tolerance at the physiological and genetic level. Genetically distinct breeds are needed for research into disease resistance and susceptibility which could help in the development of better medication or management of disease. It could also help with the identification of specific genes involved in natural disease or parasite control. Some populations may also be used as research models in other species, including man. This is already the case in the use of Ossabaw Island Hogs in the USA. These feral pigs from an isolated island off the east coast of the USA have been shown to have a natural insulin disorder making them a useful research model for human diabetes (Brisbin, 1985).
3.1.3 Cultural Interest Many populations have played an important role in specific periods of national or regional history. For example, Texas Longhorn cattle in the colonization of the USA, Spanish Merino sheep in the creation of Spain's seventeenth century wealth, or llamas, important as pack animals and fibre producers for the Inca nation of Peru. There are also breeds which have been associated with social and cultural development; the Navajo-Churro sheep whose wool is essential in the production of the native rugs of the Navajo Indians in the USA, or elephants involved in the religious ceremony of the Perehera in Sri Lanka. There are also many breeds which may be conserved for their aesthetic value. These might include the strain of performing Lippizan horses in Austria, the multihorned and spotted Jacob sheep of Britain, the cork-screw horned Racka sheep of Hungary or many of the ornamental poultry breeds.
3.2 The Objectives For Conservation The idea of conserving animal genetic resources focusses on two separate but interlinked concepts. The first is the conservation of ‘genes’ and the second, the conservation of ‘breeds’ or populations.