A randomized control trial investigating the effectiveness of a commercial pneumonia vaccine (Part II): Weaned lambs

The objective of this randomized controlled vaccine field trial was to determine the effectiveness of a commercial respiratory bacterin, Ovipast™ Plus, administered to feedlot lambs at weaning, approximately 8 wk of age, to improve animal health, growth performance, and carcass traits. Lambs were weaned, weighed, and sorted into groups by sex and the previous Ovipast™ Plus vaccination status of their mother, because this is stage 2 of that ongoing trial (Gardner et al., 2023). Lambs born to vaccinated ewes were vaccinated with the Ovipast™ Plus bacterin and revaccinated 3–5 wk later. Lambs born to unvaccinated ewes were not vaccinated. During the growing and finishing phases of the trial, vaccination did not reduce pneumonia treatment rates, crude or pneumonia specific mortality rates, or improve growth rates. Vaccinated lambs had a lower carcass fat cover (P < 0.001) and a 1.33 times increased odds of yielding a Grade 1 carcass compared to unvaccinated lambs (P = 0.01). Vaccination reduced carcass fat cover and improved yield grades, but it had no beneficial effect on disease rates or growth performance, suggesting a limited economic benefit of vaccinating lambs post-weaning, which were borne from ewes vaccinated with Ovipast™ Plus during gestation.