Field Trial of Vaccination against Leptospira borgpetersenii serovar hardjo bovis in a Single New York Dairy Herd

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Dry cows and late gestation heifers were assigned randomly to receive a monovalent vaccine against L. borgpetersenii serovar hardjo-bovis at about 220 days of gestation or nothing. A second dose of vaccine was administered about 28 days later to the vaccinated group. Before the trial, the herd was determined to be infected. Five of 45 lactating animals chosen by convenience were shedding leptospires in urine by fluorescent antibody testing. The herd was milking about 2600 cows during the duration of the trial. There were 1208 animals enrolled in the trial, 601 controls and 607 vaccinates. The reproductive management of the herd was not changed during the study period. Outcome measures were first service conception rate: 27% for controls, and 36% for vaccinates, chi square test, p=0.004. Survival analysis of days to conception: 50% were pregnant at 105 days in controls, and 90 days in the vaccinated group, Wilcoxon rank sum of Kaplan Meir estimates p<.001. Overall pregnancy rate from DC305 for controls was 19%, and 21 % for vaccinates. There were nearly equal abortions after first pregnancy palpation at 35-41 days after breeding, 56 in the control group and 58 in the vaccinates. Vaccination in this herd improved reproductive performance by increasing the apparent conception risk to first service.