Higher feed costs have resulted in backgrounded cattle staying on grass longer to reach heavier weights before entering the feedyard. By the time these calves get to the feedyard at 9- to 12-months-of-age, they are primed for revaccination against major respiratory diseases.

A recent study published in Bovine Practitioner provides guidance on selecting the most effective vaccine type for these calves, based on their prior vaccination history. Specifically, if calves were vaccinated with a modified-live vaccine at weaning, the study found that using an inactivated vaccine at feedlot arrival provides better protection than an MLV.

The study monitored a group of 145 calves that had received an MLV vaccine at one- to two-months-of-age. The calves were revaccinated with the same MLV vaccine at weaning. Approximately five months later, the calves were divided into groups. One group received the same MLV they had received as calves. Another group received an oil-adjuvanted, inactivated vaccine.

Following the final vaccination, calves in the group that had been revaccinated with the inactivated vaccine had significantly higher titer response for IBR, BRSV and BVDV Types 1 and 2. A higher titer response for these diseases on feedlot arrival has been associated with a reduced risk of BRD and increased weight gain.

In reviewing previous published studies, the report in Bovine Practitioner also indicates that vaccinating nursing calves with a combination of MLV and inactivated vaccines may induce a better response than using either vaccine type alone. An inactivated vaccine may be more effective to booster an MLV because it can provide a more consistent humoral immune response, resulting in higher antibody levels than produced by an MLV vaccine.

Conclusions of the study include that vaccinating backgrounded cattle with an inactivated vaccine may reduce morbidity associated with bovine respiratory disease at the feedyard. 

Source: Royan G. Comparison of the BVDV, BHV-1 and BRSV Anamnestic Response to Modified-live or Inactivated Vaccines in Calves Previously Vaccinated with a Modified-live Virus Vaccine, The Bovine Practitioner, Spring 2009.