Why is genetic diversity in animals worthy of preservation? After all, if one has selected a super-breed of sheep that e.g., produces the best wool/expenditure ratio, why would one raise animals with suboptimal ratios? On the face of it, that doesn't make economic sense.
There is nothing wrong with doing that - in the short term. But, over time, you can expect that animals will be exposed to novel environmental challenges, e.g., changing climate, or food types, or newly evolved pathogens. Natural populations face these challenges by exploiting their existing genetic variation, changing in subtle ways to adapt to changing environmental conditions. By reducing genetic variation in a population, one is effectively reducing its ability to adapt to its environment.
Mol Ecol. 2008 Jan;17(1):275-84. Epub 2007 Oct 8.
Are cattle, sheep, and goats endangered species?
Taberlet P, Valentini A, Rezaei HR, Naderi S, Pompanon F, Negrini R, Ajmone-Marsan P.
For about 10 000 years, farmers have been managing cattle, sheep, and goats in a sustainable way, leading to animals that are well adapted to the local conditions. About 200 years ago, the situation started to change dramatically, with the rise of the concept of breed. All animals from the same breed began to be selected for the same phenotypic characteristics, and reproduction among breeds was seriously reduced. This corresponded to a strong fragmentation of the initial populations. A few decades ago, the selection pressures were increased again in order to further improve productivity, without enough emphasis on the preservation of the overall genetic diversity. The efficiency of modern selection methods successfully increased the production, but with a dramatic loss of genetic variability. Many industrial breeds now suffer from inbreeding, with effective population sizes falling below 50. With the development of these industrial breeds came economic pressure on farmers to abandon their traditional breeds, and many of these have recently become extinct as a result. This means that genetic resources in cattle, sheep, and goats are highly endangered, particularly in developed countries. It is therefore important to take measures that promote a sustainable management of these genetic resources; first, by in situ preservation of endangered breeds; second, by using selection programmes to restore the genetic diversity of industrial breeds; and finally, by protecting the wild relatives that might provide useful genetic resources.