marker-assisted selection in wheat - ictsd

Chapter 13 – Marker-assisted selection in sheep and goats 233a significant return on overall investment ingenetic improvement. Also, in some moreadvanced sheep breeding programmes,the use of artificial insemination (AI) andacross-flock evaluation has boosted the useof high profile rams and raised the value ofindividual breeding animals.The main investment in breeding programmesis for performance recording.The extent of trait measurement is oftenquite closely aligned with the intensity ofthe production system. Input levels forsheep production vary, depending on breedtype and market. In Australia, for example,there is a significant difference betweenwool producing Merino sheep that arekept extensively in harsh environments,and more intensive lamb production systemsthat are found in higher rainfall areasor on irrigated land. The proportion ofbreeding flocks for which objective traitand pedigree measurements are undertakenis relatively much higher in the Australianterminal sire breeds.Selection takes place within the breedingstuds. AI is common in the stud breedingsector, enabling the genetic linkage of flocks.There are breeder groups with organizedprogeny testing of young sires across flockprogrammes. In Australia, a national geneticevaluation system known as “Lambplan”has driven genetic evaluation for terminalsires and maternal breeds across flocks formore than a decade. Breeders as well as rambuyers are increasingly basing their ramassessment on estimated breeding value(EBV) or dollar index value. Such a systemgives breeders incentives to invest in traitmeasurement and to create genetic linksbetween their flocks, otherwise it wouldbe difficult for a ram to rise to the top ofthe across-flock EBV list. Hence, there isincreasingly an exchange of genetic materialbetween flocks, mainly through the useof AI. Obviously, such a breeding structurewould be more conducive to breedersinvesting in gene marker technology.By contrast, the Australian Merinoindustry has had a much lower proportionof breeders taking up trait and pedigreerecording. The industry is more traditionaland selection is most often based on visualassessment. While this might be due partlyto the sector being more extensive, AIhas been commonly used in the Merinostud sector and top Merino rams havealways been sold for high prices. Therefore,the extensive nature of the industry doesnot fully explain the lack of investmentin performance recording. The traditionalnature of the industry that has hamperedthe uptake of quantitative genetic principlesis also the result of socio-economic factors,with wool producers being traditionallya prominent and relatively wealthy socialclass. The lamb industry has long beenthe wool person’s “poor brother”, but thislack of status has accelerated innovationwith the introduction of new approachessuch as formal recording and across-flockevaluation. Hence, economic as well associal and cultural reasons may explainwhy sheep breeding programmes havedifferent levels of sophistication in termsof recording, genetic evaluation and acrossflockselection.Breeding programmes and traitstargetedMeat sheepLarge-scale genetic evaluation programmesfor sheep are found in Australia, France,New Zealand, South Africa and the UnitedKingdom. In all of these, performancerecording for meat traits is well advanced,with not only weight traits measured, butalso traits related to carcass quality such asbody fat and muscle (based on ultrasound