Comparing respiratory disease treatment rates in preconditioned calves vaccinated with 4-way killed or modified-live virus vaccine

Abstract

This prospective longitudinal study was conducted in a commercial backgrounding operation to compare bovine respiratory disease (BRD) treatment rates of 2 groups of 491 lb (223 kg) preconditioned feeder calves (n=772) during 2 backgrounding periods (average 134 days). The preconditioning program was the same for both groups of calves, with the exception that 1 group was vaccinated prior to delivery with 4-way killed-virus (KV) respiratory vaccine, and the other group with 4-way modified-live virus (MLV) respiratory vaccine. Assessment of vaccine efficacy was determined by BRD treatment rates during the backgrounding periods. Results demonstrated a treatment by weight interaction, as calves at the 25th percentile of the population for initial weight and vaccinated with MLV respiratory vaccine had a significantly (P=0.03) lower treatment rate compared with calves at the 25th percentile that were vaccinated with KV vaccine. Over both backgrounding periods, 66 of 380 calves (17%) that received KV vaccine were treated for disease and 56 survived, whereas 17 of 381 calves (4%) that received MLV respiratory vaccine were treated and 9 survived. An analysis of risk factors showed that the relative risk that calves receiving KV vaccine would require treatment for BRD was 26% higher than for calves receiving MLV vaccine; that 74% fewer calves were treated for BRD when MLV vaccines were administered; and that for every 8 calves vaccinated with MLV vaccine, 1 fewer calf would require treatment for BRD than if the same number of calves were vaccinated with KV vaccine.