Bovine leptospirosis: some clinical features of serovar hardjo infection.

During an investigation of natural in utero infection of cattle by Leptospira interrogans strains, infection (almost entirely caused by serovar hardjo) was diagnosed in 57 per cent of 505 calves (472 aborted fetuses, 20 stillborn calves and 13 perinatal deaths) examined over a six-year period. The prevalence of leptospire-infected fetuses showed a seasonal increase in September, October and December and was significantly higher in fetuses aborted by dairy cows than in fetuses aborted by beef cows. The majority of infected fetuses were aborted from the sixth month of gestation onwards. Cows which aborted infected fetuses had not previously exhibited overt signs of agalactia. There was an association between leptospiral infection and retention of fetal membranes.