Experimental neonatal colibacillosis in cows: immunoglobin classes involved in protection.

Pregnant cows were vaccinated with one of four vaccine preparations to induce passive immunity in their offspring against a homologous oral challenge with Escherichia coli strain B-44. Quantitative assays of specific antibody in colostral whey from both immunized and nonimmunized dams revealed that immunoglobulin G, immunoglobulin A (IgA), and immunoglobulin M (IgM) with anti-O (somatic) activity were present in whey of all dams tested, whereas a marked deficiency of IgA and IgM anti-K immunoglobulin was noted in the whey from control dams only. The degree of scours (neonatal colibacillosis) induced by oral challenge was evaluated clinically and reported by a semiquantitative scour index as 0 to 4+. Calf scour indexes showed an inverse relationship to the frequency of occurrence and to the levels of IgA and IgM in whey of dams vaccinated with killed vaccine, live vaccine, and culture supernatant, and from nonvaccinated controls. The data strongly suggested that IgA and colostral IgM anti-K immunoglobulins were important in passive immunity in experimental neonatal bovine colibacillosis.