The investigations described were designed to identify the cause of serological reactions to Leptospira interrogans serovars hardjo and sejroe in Canadian cattle, and to confirm by culture a diagnosis of leptospirosis in cases of reproductive failure and atypical mastitis.Leptospires were detected in ten of 64 urine cultures, nine of 18 kidney cultures, and one of nine cerebrospinal fluid cultures. Twelve strains were purified. All were placed in the serogroup which contains serovars hardjo and sejroe. The nine strains which were fully serotyped were considered to be identical with serovar hardjo strain hardjoprajitno. Hardjo was isolated from cattle in the presence or absence of clinical disease and of antibody detectable by the microscopic agglutination test. Hardjo antigen was more sensitive than sejroe in detecting agglutinins in 58% of actively infected cattle and equal in 25%, as shown by comparative serum titrations.
