Health and performance of young dairy calves vaccinated with a modified-live Mannheimia haemolytica and Pasteurella multocida vaccine

Objective-To evaluate the health and performance of young dairy calves vacc inated with a commercial Mannheimia haemolytica and Pasteurella multocida v accine. Design-Randomized clinical trial. Animals-358 Holstein dairy calves between 14 and 20 days of age on 8 farms. Procedure-Calves were randomly assigned to a control or vaccinated group. T he vaccine used was a commercial modified-live M haemolytica and P multocid a vaccine that was administered on days 0 and 14. Calf weight was measured on day 0 and monthly for 3 months. Farmers were asked to record any treatme nt given to the calves and the reason for treatment during the 4 months of the study. Blood was collected from all calves on days 0 and 28, and titers of antibodies to M haemolytica were determined by means of direct bacteria l agglutination. Results-Mean daily gain was not significantly different between vaccinated and control calves. Vaccinated calves had a significantly greater increase in antibody titers (5.3-fold increase), compared with control calves (3.6-f old increase). There was no significant difference between vaccinated and c ontrol calves for any of the treatment outcomes (number and duration of tre atments and age at first and last treatments). Conclusions and Clinical Relevance-Results suggest that the M haemolytica a nd P multocida vaccine, given twice 2 weeks apart, was effective in increas ing titers of antibodies against M haemolytica in young dairy calves but di d not improve calf performance or health.