Infertility and abortion among first-lactation dairy cows seropositive or seronegative for Leptospira interrogans serovar hardjo

Objective - To estimate the extent to which exposure to Leptospira hardjo before or at the time of first parturition was associated with infertility and abortion during the first lactation among dairy cows that had not been vaccinated for ≥ 12 months. Animals - 207 first-lactation cows from a herd of 2,000 lactating cows. Procedure - Cows were tested for antibodies to L hardjo within 40 days after calving. Time from calving to first breeding, time from calving to conception, number of breedings per conception, and risk of abortion were compared between cows seropositive for L hardjo and cows that were seronegative. Results - For the 9 (4.3%) cows that were seropositive for L hardjo, median time from calving to conception (132.6 days) was significantly longer than time for seronegative cows (95.4 days). Cows that were seropositive were twice as likely (relative risk, 2.07) to fail to conceive as seronegative cows. Mean number of breedings required per conception for seropositive cows (3.4) was significantly higher than that for seronegative cows (2.1). The proportion of seropositive cows that aborted was not significantly different from the proportion of seronegative cows that aborted. Conclusions and Clinical Relevance - Exposure of nonvaccinated dairy cows to L hardjo can be associated with a subsequent reduction in fertility, as indicated by a greater time from calving to conception and higher number of breedings required per conception. The efficacy of leptospiral vaccines should be assessed to determine whether vaccination will minimize herd infertility associated with L hardjo infection. (J Am Vet MedAssoc 1999;215:515-518).