In the conditions of the Republic of Belarus there was analyzed the influence of the following paratypical factors on cow productive longevity: age of the first calving; milk yield at the first lactation; and a birth season. At the experimental animals there studied the indices of dairy efficiency: a lifelong milk yield (kg); a lifelong yield of dairy fat (kg); the total duration of the lactation period (days); duration of practical use (lactations). There was noted a tendency of increasing of a term of productive use and lifelong productive efficiency at the animals the practical economic use of which was begun in later terms. The insemination of these animals was approximately realized at the age older than 21 months. Also it was stated that in accordance with all investigated indices (except for a milk yield per one day of lactation) the highest indexes were typical for cows which had the least milk yield at the first lactation.

Development of new compositions of premixes for cows with milk yield of 4-5 thousands kg per lactation depending on lactation stage and pregnancy was realized in the conditions of the Republic of Belarus. Efficiency of application of premixes in comparison with the standard ones was estimated. Experiment was realized by an example of 3 groups of cows of white-and-black breed; experimental period included beginning milking period (90 days) and the main lactation period (142 days). Cows of the first control group were given premix P60-6M with combined feed. Animals of the second group were fed with premixes created on the basis of carotene and microelements content. Cows of the third group were given premixes in accordance with recommended standards. The refined standards of cow vitamin and trace elements consumption were presented. Formulas of premixes for high-producing cows were presented. The research results showed that the developed formulas corresponded to the physiological needs and their application influenced on metabolism and milk producing ability. Application of experimental premixes made it possible to increase the digestibility of nutritive substancesoin 2,3-7,5%. Application of vitamins and trace elements in heightened doses (on 10-30%) caused the increasing of their uptake and increasing of cuprum, zinc, manganese and cobalt content in blood on 11,6-40,8%

Factors which increased milk productivity (age and continuance of service period) were studied in the conditions of an educational establishment of the Republic of Belarus by an example of cows of black-and-white breed. Dynamics of growth of milk productivity in course of 8 research years was presented. Analysis of interrelation between cow productivity and cow age was given. Mathematical calculation of relations between cow productivity indexes (milk yield, fat content, butter fat) and service period duration was given. Research results showed that increasing of an average term of economic use of cows and decreasing of duration of service period up to 90 days made it possible to increase dairy effiiemcy and herd reproduction, as well as obtain higher economic efficiency