Two commercial live virus
infectious bovine rhinotracheitis (IBR)
vaccines for
intranasal administration and an inactivated polyvalent calf
pneumonia vaccine were compared for safety and efficacy in calves against experimental IBR
infections. All three products were clinically safe for use in young calves; a mild, transient, febrile response was induced by one of the live
vaccines. Vaccinal virus was recovered for up to 16 days after vaccination from nasal secretions of all calves given live
vaccine. Both live
vaccines stimulated a serum neutralising antibody response, but the
inactivated vaccine failed to elicit any serological response. Following intranasal challenge four months after the first dose of
vaccine, all live virus vaccinates remained systemically healthy. A slight nasal discharge and a few rapidly healing
ulcers of the nasal mucosa were the only abnormalities observed. Both the group given the
inactivated vaccine and the unvaccinated controls developed clinical IBR with
pyrexia, ocular and nasal discharges, severe ulceration of the nasal mucosa and
tracheitis and tachypnoea to varying degrees of severity. Parenteral administration of
dexamethasone six months after challenge induced reactivation of virus shedding followed by a rise in humoral antibody titre irrespective of the original vaccination history.