Immunization of calves and herd immunity to Bovine Respiratory Disease Complex (BRDC)

Abstract

Vaccination practice is one of the main tools to control Bovine Respiratory Disease Complex (BRDC). Since wide spreading and serious damages related to BRDC, immunization to respiratory pathogens should be considered a core vaccination in either dairy or beef cattle operations. Vaccination to BRDC should be planned following a program of immunization. Systematic immunization of the animals towards respiratory pathogens is pivotal to control BRDC reducing clinical signs and pathogen spreading. Pathogens target of vaccination, type of vaccine, vaccination timing and route of vaccine administration should be of concern to plan an effective vaccination program aimed at getting herd immunity to BRDC agents. The percentage of animal to be vaccinated at obtaining herd immunity to a specified pathogen is named critical proportion and it depends from the vaccine impact (efficacy) and the basic reproduction ratio of the pathogen. Calves are highly susceptible to BRDC agents, therefore to get herd immunity it’s necessary to set up a vaccination program including immunization of young animals. Since vaccination is a preventive measure, the pathogen calves will encounter firstly should be the target of the first vaccine treatment. Both diagnostic and herd history offer an opportunity to make a correct choice. It’s known that maternally derived antibodies trigger a strong interference to get a robust adaptive immunity through vaccination. Therefore, the optimal age for the first vaccination depends from the duration of maternal immunity, assuming an exponential decay in the fraction maternally protected as host age, and the mean host lifespan in years. Once got herd immunity, it must be kept overtime by adopting the repeat-pulse vaccination strategy. In accordance to duration of immunity elicited by the vaccine, the period of time that elapses between two consecutive vaccination can be calculated assuming the mean lifespan of the population to be vaccinated, the vaccine impact and the basic reproduction ratio of the pathogen. At any rate, the golden rule remains to set up an immunization program tailored for a herd. At the aim it’s necessary collaboration of farmer and veterinarian, as regards the instructions of the vaccine producer.