marker-assisted selection in wheat - ictsd

232Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishcurrently most real applications of MASfor sheep and goat breeding are based onresearch projects and therefore subsidized.However, the first commercial applicationsare now also emerging. The main requirementsfor a successful commercial andlong-term application of MAS in sheep andgoat breeding are discussed and illustratedbased on examples.MAS applications are often illustrated orsimulated for pure breeding programmes.However, MAS could be particularlyuseful in crossbreeding programmes wheredesirable genotypes in unfavourable backgroundsare introgressed into productivelocal breeds with overall better breedingvalues. The opposite is also possible, wheredisease resistance genes of local breedsare specifically targeted in upgrading programmeswith imported stock with higherproductivity being crossed to local breeds.Crossbreeding and introgression programmesare discussed and, as sheep andgoat production is relatively predominantin developing countries, particular attentionis given to breeding programmes forlow to medium input production systems.Characteristics of sheep andgoat breeding programmesBreeding structuresBreeding programmes for sheep and goatsgenerally operate within an industry that isbased on low levels of resource inputs, i.e.low levels of feeding and low labour costson a per animal basis. Goat production takesplace largely in developing countries whereselective breeding based on performancerecording is often absent. A more substantialproportion of sheep production is foundin developed countries such as Australia,France, New Zealand, South Africa and theUnited Kingdom. These systems are alsopredominantly pastoral-based and extensivein nature. An FAO working group report(Hoste, 2002; Olivier et al., 2005) made thefollowing distinction between productionsystems and the opportunities within themfor breeding programmes: 1) subsistencebasedproduction, among the world’spoorest, with limited market developmentand limited inputs and scope for geneticimprovement; 2) market-based production,with better developed markets targetingurban populations, higher input levels andmore specialized production systems, withscope for genetic improvement dependingon cost of inputs and also on skills andinformation literacy of breeders andproducers; and 3) high-input production,with further specialization, emphasis onincreased land and labour efficiency, andmuch more concern for food quality, foodsafety, animal welfare and the environment.Most of the world’s goat production aswell as many of the sheep systems wouldfall into the first category, whereas sheepproduction in developed countries wouldmainly fall into the second category, withsome of these working towards the thirdcategory.Sheep and goat breeding programmes arecharacterized by a flat breeding structure,meaning that compared with intensivelivestock industries many operationsparticipate in genetic improvement, therebyforming a wide base for the nucleus breedingsector. Reproductive levels of breedinganimals, especially males, are relatively lowcompared with other species. In such asystem, the multiplication factor, i.e. thenumber of commercial expressions resultingfrom investments in improved genotypes inthe breeding nucleus, is relatively low. Thismakes it more difficult to introduce newtechnologies and justify large investments inimproving individual animals. However, likeother breeding programmes, there remains