In building up highly productive egg laying strains of hens and in subsequent work with them correct evaluation and purposeful selection of sires is of high importance.

Until recently evaluation and selection of cockerels for conformation and their mothers’ productivity were the principal methods used although the coefficients of correlation between the productivity of cockerels’ mothers and that of their daughters are not high. This is because their mothers’ phenotypic performance depends not only on the genetic contribution but also on the effects of environment. The latter plays a considerable role in either checking or realising the genetic potential.