One of the conditions for increasing the efficiency of milk production is the modernization of farms with the introduction of technologies for loose maintenance and maintenance of livestock. Mainly the transition to a loose-fitting content allows to significantly reduce labour costs and the number of employees, to facilitate the work of operators directly servicing animals. At the same time, problems of mechanization and automation of processes are more easily solved. Productive longevity, expressed as the number of lactations per year or the milk yield per year during the lifetime, is a function of three or four variables: age at the first calving, calving interval, number of lactations during the lifetime and, respectively, milk / fat / protein yield in the standard lactation. Because these two functions are not linear, their expressions are approximated as linear functions of the considered variables. These functions express the phenotypic value of the trait, the number of lactation per year or the milk yield per year during the lifetime. Each of these functions is used to define an aggregate genotype. The calculated aggregate genotypes put together usual traits, which are difficult to be used in an index-based selection. If these traits are genetically evaluated, the selection index for an animal results directly from the aggregate genotype by replacing the true breeding values with the estimated breeding values. The expected number of lactations may substitute the number of lactations of a cow, which did not finish its career
