The effect of Escherichia coli J5 and modified live Salmonella dublin vaccines in artificially reared neonatal calves

One thousand neonatal calves, allocated in a factorial design into four groups, were vaccinated subcutaneously with two doses each of either killed Escherichia coli (O111:B4) J5 bacterin or a UC Davis modified live, genetically altered (aro^-) Salmonella dublin vaccine, or both, or with a placebo. In this prospective double-blind study to determine the immunogenicity and protective effects of both vaccines on bovine neonates in field conditions, calves were observed daily until 2 months of age, and serum samples from selected study calves were obtained at five different time points. No clinical adverse vaccine reactions were observed. Overall mortality was 7.5% (75 of 1000), E. coli and S. dublin infection being the most commonly associated aetiological agents of deaths. Both J5 (p<0.01) and Salmonella (p=0.05) vaccines were significantly effective in reducing the mortality rate but without an additive effect. The role of passive transfer was important in calf survival. The E. coli J5 and (aro^-) S. dublin vaccination schedule employed significantly (p<0.001) elevated J5 and Salmonella-specific serum ELISA antibody titres, respectively, by the sixth week of age.