Utilisation of genetic variation by marker assisted selection in commercial dairy cattle populations

Potential genetic benefits of marker assisted selection (MAS) were evaluate d by calculating selection response resulting from four pathways of selecti on. Genetic variation was partitioned into polygenic and loci that were in linkage disequilibrium with marker loci or haplotypes. The percentage of ge netic variation that was marked was varied from 0 to 100%. These assumption s describe the degree of genetic knowledge that may be available in 10 year s. Three breeding strategies with markers were evaluated: progeny test sche me (BMARK); progeny test scheme but unproven bulls allowed on the bull to b ull selection path (YBULL); and a breeding programme where cows without lac tation information and bulls without progeny information were eligible for selection (OPEN). Rates of genetic gain (per year) with no marked genetic v ariance were 0.26 sigma(G) for the BMARK and YBULL schemes and 0.28 sigma(G ) for the OPEN scheme. On average, an increase of 1% marked genetic varianc e resulted in an increase in genetic gain of similar to 0.25% for the BMARK scheme, 0.5% for the YBULL scheme and 1% for the OPEN scheme. Maximum gene tic response (100% marked genetic variance) for the BMARK scheme was 1.24 t imes that achieved with no marked genetic variance, 1.52 times for the YBUL L scheme, and 2.05 times for the OPEN scheme. Changes in the structure of t he breeding scheme are needed to fully gain the benefits of identified loci especially for medium to large proportions of marked genetic variance. (C) 1999 Elsevier Science B.V. All rights reserved.