12.1 Genetic improvement in a breeding program
- Tessa Jacobs
- Kor Oldenbroek
As we have seen before, the permanent selection response depends on the selection intensity, the accuracy of the breeding value, the genetic variation and the generation interval. The first three are in the nominator of the formula and the last one in the denominator. Thus a higher the selection intensity, accuracy and genotypic variation and a lower generation interval gives the highest response. The formula is:
where: SR = selection response; i = selection intensity; r = accuracy; varg = genotypic variation and GI = generation interval
Within a breeding program the genotypic variation can hardly be influenced, but the other three parameters can be influenced. They are interrelated especially the accuracy of selection and the generation interval. E.g. a choice can be made for selection with a high accuracy, but you have to wait a long time before you have all the information of the selection candidates resulting in a long generation interval. When the choice is for a lower accuracy, you may select younger animals for breeding, resulting in a short generation interval. Thus breeding programs can be optimized with respect to selection intensity, accuracy and generation interval.
As shown before, within a breeding program the selection response can be generated in four different selection paths. The total selection response is the addition of the selection response in these four different paths, with in the following order, a decreasing impact on genetic improvement: sires to breed sires, sires to breed dams, dams to breed sires and dams to breed dams. In the structure of breeding programs these differences in impact are reflected in the structure.