The incidence of leptospirosis due to L. pomona and L. hardjo in 900 cattle at the Dixon Springs Agricultural Center was evaluated annually by the microscopic agglutination test during a 15-year period.

The L. pomona reactor rate ranged from 5 percent in 1954 to 58 percent in 1955 during the period from 1953 to 1958 when the cattle were not vaccinated. Abortions were observed during 1955 and 1960.

The L. pomona reactor rate ranged from 15 percent to 28 percent between 1959 and 1964 when half of the cattle were vaccinated and declined to 0.5 percent to 5 percent when all of the cattle were vaccinated with L. pomona bacterin.

An infection of L. pomona vaccinated cows occurred in 1968 as indicated by a MA titer response of 1:100. No clinical signs were associated with the infection. The infection may have been caused by an endemic infection in a few carrier cattle or from infected wildlife. The skunk had previously been shown to be an active shedder.

The L. hardjo reactor rate ranged from 29 percent to 56 percent during the period from 1958 to 1966 when the cattle were not vaccinated and 33 percent during 1967 and 1968 when half of the cattle were vaccinated.