Field trial evaluation of a reo-coronavirus calf diarrhea vaccine.

Field trials were conducted using an experimental, modified live virus, oral vaccine for prevention of reo- and coronavirus calf diarrhea. Prior to the trials, one or both of the specific causative agents were identified from affected calves in each participating herd. In 21 herds, sequential trials were conducted in which results of uninterrupted vaccination were compared with disease rates during a preceding or subsequent control period. In these herds there was a statistically significant reduction in the morbidity and mortality from disease in 1,598 vaccinates compared with the rates in 829 prevaccination control calves. Morbidity and mortality in 206 post-vaccination control calves rose marginally above the rates in the same vaccinates. In 26 other herds, where double blind trials were conducted, rates of morbidity and mortality from disease were virtually the same for 1,080 vaccinated calves and 355 placebo calves. Vaccinates in the sequential trials had the lowest morbidity and mortality rates of any test group in either field trial format. In a selected dairy herd, both field trial formats were implemented and the results compared. In the double blind trial, vaccinates and placebo calves had comparable rates of morbidity and mortality from disease. When a sequential trial was later implemented, a statistically significant reduction in morbidity and mortality occurred in vaccinates compared with rates in control calves.