Pre-selecting young bulls before progeny-testing with marker-assisted BLUP

Suppose that a QTL affecting milk production trait of dairy cattle has been identified, and the relative dis-tances between the QTL and the markers are known without error. The relative efficiency of pre-selection of young bulls before progeny-testing with marker-assisted BLUP (MBLUP) over conventional progeny-testing (i.e. random selection be-fore progeny-testing) for five generations was studied using Monte Carlo simulation. Different numbers of QTL alleles (two or infinite), initial frequencies of the favorable QTL allele (0.1 and 0.5, when the QTL has two alleles), distances between the adjacent markers (5 cM or 20 cM), and ratios of the QTL variance to the genetic variance (10%, 25%, and 50%) were considered in the simulation. The results showed that the relative efficiency of MBLUP was higher when the marker distance was 5 cM than that when the distance was 20 cM. The larger the QTL allelic effect, the lower the MBLUP efficiency. The relative superiority of MBLUP was higher when the QTL had two alleles and the frequency of the favorable QTL allele was low in the base population. The relative superiority of MBLUP decreased with the pro-gress of generation in all cases and the decreasing rate was getting higher with the increase of marker density and QTL effect.