9.12.2 Realizing the selection response in dairy cattle (2024)

In dairy cattle breeding the prediction of the selection response in the breeding population becomes a bit more difficult as the majority of the cows used for milk production are owned by individual farmers. Each farmer will have his or her own breeding goal, though in general terms these will resemble that of the breeding company, who owns the bulls. The breeding companies know what the farmers want and need. The selected proportion in bulls is in the hands of the breeding company. They provide the (genomic) breeding values. The farmers can decide which bull they use. The assumption when predicting genetic response to selection is that all selected bulls will have equal chance of ‘spreading their genes’. This obviously is not the case in the real world. Depending on which bulls are used more often than expected, this will lead to an over or under prediction of the genetic response. On the females side there may be very little effect of selection in cows for two reasons: first of all the selected proportion is very large as most cows are used to produce replacements. Second, the farmers may have slightly different selection criteria that result in an overall even smaller effect of selection in the cows. In practice, this selection path can be ignored.