Thus far we have been discussing the optimal situation in which someone decides on which animals are allowed to breed and which are not. There are two main points where the breeder has influence: the selected proportion and the accuracy of selection. For good predictions of the genetic response it is essential that the assumptions for the selected proportions and the accuracy of selection are correct. This is not always the case and is different in the different species as will be outlined in the subparagraphs for pigs and poultry, dairy cattle, horses and dogs.
So what to do with these situations where selected proportion and accuracy of selection cannot be established very well? One solution can be to predict the average genetic potential in the offspring of each mating based on the EBV of the sire and the dam. As we have seen in the chapter about genetic models, knowing the EBV in the parents only gives you some idea about the EBV in the offspring due to the Mendelian sampling: Aoffspring = ½ Asire + ½ Adam + MS. It will depend on the accuracy of the EBV in the parents to what extend the inaccuracy of the prediction of the genetic response will be further increased.
In conclusion: predicting genetic response to selection assuming a selected proportion and an accuracy of selection is very useful, but be aware of the (lack of) accuracy of your assumptions!