Duration of lactation and economic use of highly productive black-motley cows

Intensive growth of cow productivity in dairy cattle breeding leads to an increase in the duration of lactation. At the same time, the average age of cows in dairy cattle populations tends to decrease. In this connection the purpose of the research was to study the influence of the duration of the first lactation on the indicators of productivity, duration of economic use of highly productive cows and determine the optimal number of dairy days in the first lactation for a more effective use of animals. The research base was formed with the information-analytical system “SELEX. Dairy cattle”. The analysis includes data on milk yield during the whole lactation and 305th days of the first lactation, service-period during the first lactation, number of dairy days during the first lactation, age of animals at calving, lifetime productivity of 328 cows of the black-motley breed that were retired. A reliable (P ≤ 0.001) close correlation of lactation duration with milk yield for the whole lactation (r = +0.82) and service period (r = +0.90) was established. A reliable (P ≤ 0.001) moderate strength relationship between the duration of lactation and productivity for 305 days (r = 0.30) was revealed. The influence of the degree of milk yield drop per lactation on the duration of lactation was determined, which is confirmed by reliable (P ≤ 0.01) positive correlation (r = +0.16) with the coefficient of lactation stability. It was found that the duration of the first lactation has a negative reliable (P ≤ 0.001) relationship of moderate strength (r = -0.34) with the age of cows that have calved. A more accurate measure of the duration and efficiency of a cow use in a herd is life expectancy in days and milk yield per one day of life. Studies have shown that increasing the duration of first lactation for more than 360 days is ineffective. Duration of lactation from 301 to 360 days is optimal. Cows with such duration of the first lactation have the highest lifetime milk yield, longevity, and milk yield per one day of life.