A diffusion in gel-enzyme linked immunosorbent assay (DIG-ELISA) was used to record immunoglobulin development of colostrum-fed calves vaccinated with aromatic dependent (aro-) Salmonella and challenged with either the homologous or a heterologous serotype. IgG was detected by using a peroxidase conjugated rabbit antibovine IgG, whereas IgM and IgA were measured using a double sandwich technique. Although IgG levels to Salmonella endotoxins increased after exposure to Salmonella, they were found to be high in many calves prior to vaccination. However, IgM antibody levels were consistently low prior to vaccination, and their increase was a more reliable indicator of the vaccination and immune status of the calves. IgA levels were generally low and of less predictive value.
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