Vaccination of cows with a K99 extract to protect newborn calves against experimental enterotoxic colibacillosis.

Pregnant cows and heifers were vaccinated with a crude K99 extract prepared from an Escherichia coli K-12, K99 strain. A similar group, injected with an extract prepared from the K-12 parent strain, served as a control. Eleven calves were born to both groups and challenged orally with a mean of 1.6 x 10(11) bacteria of enterotoxic E. coli B41 (O101:K99+, ST+) at the time of first colostrum uptake (1 to 7 h after birth). As a result of challenge, no death occurred in the vaccine group, but four calves died in the control group. Six calves in the vaccine group and all calves in the control group developed diarrhea. Colostral anti-O101 titers were very similar in both groups. Anti-K99 titers of colostral samples from the vaccinated dams were, however, significantly higher as compared to those of the controls. It is suggested that colostral antibodies, raised against the crude K99 extract vaccine, exerted a protective effect on newborn calves against the challenge enterotoxigenic E. coli O101:K99+, Ent+ strain.