A total of 255 cows were observed for up to five preg-nancies; 69 of them were seropositive, 171 seronegativeand 15 changed their sero-status during the experiment.Among seroconverted animals, six (2.4%) cows that werefound negative in the first examination became positiveduring the experiment; four were initially found positive,but became negative at two or three subsequent timepoints; five cows showed fluctuating titers, being mostlypositive, but negative at some points. The 15 seroconverted animals were excluded from the analyses in consecutive pregnancies. As shown in Table 3, in 69 seropositive dams,a total of 34 (49.3%) aborted. In contrast, abortion occurredin 29 out of 171 (16.9%) seronegative dams (p < 0.0001). Inseropositive cows, the number of abortions became higheras the number of observed pregnancies increased from41.1% abortions at 2 gestations to 45.8% and 77.7% at 3 and 4 pregnancies, respectively. Among the 171 seronega-tive cows, the percentage of abortion was 15.1%, 13.5% and36.4% when followed for 2, 3 and 4 pregnancies, respec-tively. Only four cows (2 positive and 2 negative) werefollowed up during five consecutive years. All of these cowshad aborted.