Comparison of dairy cows with low or high rate of udder infection

Within farms, animals with low and high rate of udder infection were selected from data of a mastitis-prevention field experiment during 3.5 years. Differences between the groups in udder conformation and milkability appeared to be small but were consistently to the disadvantage of the high infection rate group. In the course of a least three preceding lactations the percentage of quarters infected at any time was 53 per cent in the low and 91 per cent in the high infection rate group. The number of infections per quarter infected was 1.53 for the low infection rate group and 2.53 for the high infection rate group. As compared with infection-free quarters it was shown that the duration of infections with udder pathogens was significantly shortened if a quarter was already infected with secondary, i.e. less or non-pathogenic, bacteria. It was not possible to demonstrate differences in cell count or immunoglobulin levels in infection-free quarters between the low and high infection rate groups.