Passive protection of lambs against enteropathogenic Escherichia coli: role of antibodies in serum and colostrum of dams vaccinated with K99 antigen.

Lambs from suckling ewes vaccinated with the K99 antigen were resistant to challenge with K99-positive enteropathogenic Escherichia coli. Serum and colostrum from these ewes were compared with samples from control ewes to establish methods for monitoring vaccination and to determine the mechanism of protection. Vaccination stimulated production of K99 antibodies. These could be detected by an indirect haemagglutination test and a haemagglutination-inhibition test. Antiglobulin and gel-diffusion tests were less reliable. Experiments with brush-border cells from calf intestine showed that the antibodies were associated with anti-adhesive activity. The antibodies were predominantly IgG and did not neutralise the activity of heat-stable enterotoxin. It was concluded that neutralisation of the adhesive properties of the K99-positive E. coli by colostral antibodies significantly contributed to the resistance of the lambs from vaccinated ewes.