Methodical guide developed to improve the selection of dairy cattle to include lactation persistence in the breeding value index. The state and study of the persistence of milk yield and components of cow milk were considered, new approaches for calculating the value of the trait were proposed, standard models for lactational curves of dairy cattle of Simmental and black-and-white breeds were developed. The heritability and variability of persistence indicators were studied, the breeding value of animals was estimated by the level of yield and the persistence indicator. Models of lactation curves and an estimated indicator on the basis that best reflect the relationship between dairy productivity and signs of reproduction. are proposed.