Demonstration of passive protection in neonatal calves against colibacillosis following immunization of pregnant heifers at 3 months of gestation.

: Enterotoxigenic Escherichia coli is one of the primary etiologic agents for diarrhea in neonatal calves. Immunization of dams can provide passive protection in neonatal calves; antibodies transferred through colostrum block colonization of bacteria, thereby preventing disease. In this study, healthy pregnant heifers were vaccinated at approximately 3 months of gestation with either a polyvalent oil-adjuvanted vaccine containing inactivated coronavirus, rotavirus, E. coli K99 subunit antigen, and Clostridium perfringens b and e toxoid or normal saline as a placebo. Calves were allowed to nurse immediately after birth, were orally challenged with virulent heterologous enterotoxigenic E. coli at 1 day of age, and were observed for clinical signs of scours for 10 days. Signs of severe scours were noted in 75% of control calves and 28.6% of vaccinates, and the severity of scours was significantly higher (P = .0382) in the control group. The mortality rate was significantly higher (P = .0007) in the control group (80%) than in the vaccinate group (14%). These findings indicate that the vaccination of pregnant heifers at as early as 3 months of gestation (6 months before calving) provides passive protection in neonatal calves against colibacillosis.