Starting marker-assisted selection in dairy cattle: a simulation study

The starting period of marker-assisted selection was investigated in a dairy cattle breeding organisation. The objective was to try and quantify the extra genetic gain occurring in the first batch of young bulls concerned by this new selection method. The genetic determinism of the trait selected was allowed to vary (heritability, fraction of the genetic variance controlled by the genes detected and number of these genes). The amount of typing within the whole population varied as well. If 20 stands for the value of one genetic standard deviation, then the extra gains found were often in the range 1-2. These modest values are not surprizing at all for technical reasons briefly commented. Finally, one should keep in mind that selecting dairy cattle is a long painstaking task and benefits of technical improvements occur very often in the mid or long term.