Genetical and some environmental influences affecting the level of leucocyte counts in the milk of cows

The progeny groups of different sires varied widely in white-cell count in milk, even after exclusion of all cows which had suffered from mastitis. The sire had a demonstrable effect on white-cell count in milk, especially during the second half of lactation. Heritability estimates of white-cell count in milk showed that values for the fourth lactation were higher than those for heifers. But at the end of lactation heritability values for 4th lactation cows and heifers were nearly equal (about 0.40). The daughter groups with high average white-cell counts mostly showed frequent mastitis. There was a high phenotypic and genetic correlation between clinical mastitis and white-cell count. Within seasons for cows which, so far known, had never mastitis, very high and very low producers had higher white-cell counts than other cows. White-cell counts increased remarkably with advancing lactation. A relation between white-cell count and ease of milking could not be demonstrated.

Increasing milking vacuum over 40 cm mercury pressure, especially at the end of lactation, or increasing pulsation to over 50 per min. tended to increase white-cells. Milking routine (man/machine ratio) affected white-cell count in the end of lactation. More cows per milker increased the number of white-cells.