Selection paths in males and females can be very different for a number of reasons. Especially because males in general can produce (many) more offspring than females, the contribution of males to the next generation can be considerably larger than that of the females. For that reason, in many species more attention is paid to selecting the males as accurately as possible. Females often are allowed to breed without, or with weak, selection criteria. In many animal species, the deviation into different selection paths is taken one step further and discriminate between males that are selected to produce new breeding males, and males that are selected for producing females. The same can be applied to the female side: females to breed new breeding males, and females to breed females. Males that have been selected for breeding are called sires, and females that have been selected for breeding are called dams.
We can thus define four selection paths:
Sires to breed sires (SS)
This is the most stringent selection path to breed new fathers of the fathers. Only elite sires make it to sire father.
Sires to breed dams (SD)
Within the sires this is a less stringent selection path. These sires will be the fathers of the breeding females (the dams).
Dams to breed sires (DS)
This is the most stringent selection path within the dams to breed new sires. Only the elite dams will make it to sire mother.
Dams to breed dams (DD)
This is the least stringent selection path. It depends on the studbook whether there are selection criteria for new dams.
Combining these selection paths into a formula:
Thus: selection response can be divided into a number of selection paths, the number depending on the number of differences in selection intensity and the accuracy of selection