Correlation of productive longevity and reproductive functions in dairy cows

Abstract

The Ural type of the domestic Black-and-White mottled breed is characterized high milk-yield rates and good suitability for industrial milking technology. The milk yield increase led to a deterioration of reproductive functions in the livestock. As a result of the research it was found that in the process of prolonged using of the cattle, the milk yield of cows regularly changes, reaching the highest rates among the mature cows by the 3rd lactation, and then gradually decreases, remaining sufficiently high and stable. The decrease of the milk yield starts from 13 kg (in the 4th lactation in comparison with the 3rd lactation) and goes to 663 kg (from 4th to 8th lactations). That decrease makes on average 132.6 kg per lactation period, or by 1.7%. The quality indicators of milk changed to the better from the 1st to the 10th lactation. The indicators for milk yield turned out to be more variable; they had a coefficient of variability from 20.7 to 17.6, which indicates a quite wide possibility of selection in the herd by this trait. The milk yield per lactation is not related with duration of service period; and increase of reproductive functions in the modern Holsteinized Black-and-White mottled cattle will not provide a negative impact on the milk yield of the cows.