Selection with control of inbreeding in populations with overlapping generations: a comparison of methods

Methods that maximize genetic response in populations with overlapping gene rations while controlling rate of inbreeding by constraining the average re lationship among selection candidates were compared. Firstly, computer simu lations of closed nucleus selection schemes showed that a two-stage optimiz ation algorithm approach, where the distribution of parents within and ther eafter over age classes was optimized resulted in different breeding scheme s than an approach that performed an iteration on this distribution. It yie lded significantly lower annual genetic gain (0.194 v. 0.223 sigma(p) units ), fewer animals selected (21.9 v. 26.4) and longer generation intervals (2 .38 v. 1.68 years) but maintained the rate of inbreeding closer to its cons traint. In large schemes, iteration may be computationally the only feasibl e method for the optimization of parents across age classes. Secondly, the use of conventional relationships for constraining inbreeding was compared with that of augmented relationships, which do not depend on the level of i nbreeding. Both relationships resulted in very similar breeding schemes, bu t the use of augmented relationships avoids correction of the current level of inbreeding. Thirdly, a constraint of the rate of inbreeding on a per ye ar basis was compared with a constraint on a per generation basis. When opt imizing per generation, the generation interval was shorter compared with a scheme where an analogous annual restriction was in place (2.01 v. 2.38 ye ars) and the annual rate of genetic gain was higher (0.214 v. 0.194 sigma(p ) units).