Efficacy afforded by the infectious bovine rhinotracheitis virus fraction of an intranasal modified live virus vaccine inforcetm 3 (ibr-pi3-brsv) in an experimental challenge model in neonatal calves

Methodology: Thirty-five, seronegative threeto eight-day-old Holstein calves were randomly assigned to a control group (n=17) and a vaccinate group (n=18) and vaccinated intranasally on day 0 with a single 2 mL dose of a placebo vaccine (containing PI3BRSV) or INFORCETM 3 (IBR-PI3-BRSV) vaccine, respectively. During the vaccination phase, the two groups were housed in separate rooms, but all animals were commingled for the fourteen-day-long challenge phase. Calves were challenged intranasally with IBR 28 days following vaccination. Efficacy was measured by comparing the development of acute IBR disease or morbidity, rectal temperatures and nasal shedding of IBR virus between groups. Post-challenge clinical observations were performed by a clinician masked to treatment group assignments. Supporting variables were post-challenge rectal temperatures and duration of IBR virus shedding in nasal secretions. All animal procedures were approved by ethical review for compliance with ANIMAL WELFARE guidelines. All laboratory testing during the study was performed without knowledge of assigned treatments or animal numbers.