Effect of a quadrivalent vaccine against respiratory virus on the incidence of respiratory disease in weaned beef calves.

We investigated the effect of vaccination of male beef calves (mean age+/-S.D.: 158+/-31 days) against bovine herpes virus (BHV-1 or IBR virus), bovine respiratory syncitial virus (BRSV), bovine viral diarrhea (BVD) virus and para-influenza (PI(3)) virus on the incidence of respiratory disease during the first forty days after weaning and entering a feed-lot in Portugal. In May 2003, Mertolenga, Preta and mixed-breed calves from 10 different beef herds, were systematically assigned (by order of entrance in a chute) to two treatment groups, before moving to a common feed-lot. One hundred and twenty five male calves were vaccinated with a quadrivalent vaccine (Rispoval 4) and revaccinated after 21-27 days while 148 herdmates were injected with saline (0.9% NaCl) on the same occasions. The incidence and severity of clinical cases of "bovine respiratory disease" (BRD) were evaluated every day during the first 40 days after entering the feed-lot. Morbidity (3% vs. 14%) and mortality (0% vs. 4%) due to BRD were significantly lower in the vaccinated group. Ten days after revaccination, the calves were treated with an antimicrobial - ending the study - after an outbreak of BRD caused a high incidence of disease in the non-vaccinated group. In conclusion, our results showed that Rispoval 4, a quadrivalent vaccine against respiratory viruses, under field conditions, reduces morbidity and mortality due to BRD in beef calves after weaning.