Variability and correlation of milk urea content with parameters of cow productivity

During the work, 24774 individual milk samples for Ayrshire cows (Karelia, Russia) with an annual milk yield of over 8.300 kg were tested (1.355 cows) every month for the last three years. The urea content averaged 32.19 mg% with a daily yield of 25.5 kg. In cows at the age of the first two lactations, the urea content was higher than for adult animals. The urea content in milk increased from 31.46 mg% to 33.56% with increasing daily yield. In summer and early autumn, urea concentration was lower than in spring and winter. A reliable positive correlation of milk urea was obtained with daily yield, lactose, negative – with protein, dry milk matter, dry non-fat milk residue, the number of somatic cells, and lack of connection was with fat and the freezing temperature of milk. The bull's genotype has a significant effect on the amount of milk urea. Heritability coefficient (h2) was in the range of 0.222 - 0.367