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Leptospirosis is a common cause of abortion and infertility of cattle worldwide. More than 200 serovars of Leptospira have been identified, each of which is supported within its own maintenance host. The severity and chronicity of disease caused by organisms of the genus Leptospira depends on whether infection is taking place in the maintenance host (host‐adapted) for that specific serovar or an incidental host (non‐host‐adapted) [3]. Cattle are the maintenance host for serovar hardjo, which contains two genetically distinct types: Leptospira interrogans serovar hardjo type hardjoprajitno found primarily in the British Isles and Leptospira borgpetersenii serovar hardjo type hardjo‐bovis found throughout the world including North America [4, 5]. Infection of cattle with a non‐host‐adapted serovar is characterized by acute disease, late‐term abortion, and transient renal shedding of the organism. Infection with the serovar hardjo is characterized by chronic infections, prolonged renal shedding, abortion, and infertility [4]. Leptospira species are primarily shed in the urine of infected cattle. Transmission is possible via semen, and venereal transmission of serovar hardjo is thought to be common [3, 6].

Vaccination of cattle against leptospirosis is a complex and controversial subject. Many pentavalent vaccines marked for prevention and control of leptospirosis contain antigens for hardjoprajitno not hardjo‐bovis, the type most commonly isolated in North America [5]. Challenge studies evaluating the efficacy of pentavalent vaccines for protection against hardjo‐bovis have yielded conflicting data; however, these studies utilized different products and the time period from initial vaccination until administration of the booster differed greatly [7, 8]. Administration of a commercial monovalent hardjo‐bovis vaccine has been shown to prevent renal colonization and shedding of hardjo‐bovis following challenge [9]. The subject is further complicated by the true incidence of infertility that can be attributed to hardjo‐bovis. A study in California involving 207 first‐lactation cows found that cows seropositive for serovar hardjo had a mean time from calving to conception 34 days longer than seronegative cattle [10]. However, when beef cattle were vaccinated with a commercially available monovalent hardjo‐bovis vaccine and administered oxytetracycline to eliminate the carrier state of hardjo‐bovis, no improvements in pregnancy and calving rates were observed [11]. The decision to vaccinate and the product used should be based on the prevalence of leptospirosis in the area and its potential impact on reproductive performance in the herd. All the commercial vaccines currently available are killed products which should be boostered according to the label and revaccination annually is recommended.