Crossed immunoelectrophoretic analysis of the antibody response in heifers and dry cows to Peptococcus indolicus in experimental and natural heifer mastitis and dry cow mastitis

Crossed immunoelectrophoresis with intermediate gel was used to investigate the antibody response of experimentally infected heifers and of naturally infected heifers and dry cows at grass with mastitis against soluble extracellular antigens of Peptococcus indolicus. Using both precipitin titres and precipitin scores (the sum of precipitin titres against individual antigens) rising titres of antibodies against antigend of P. indolicus were demonstrated in sera from experimentally infected pregnant and non-pregnant heifers. Statistically significant differences in precipitin scores against extracellular antigens were also shown between pregnant heifers with mastitis and healthy pregnant heifers and between dry cows with mastitis and health dry cows. The biochemical nature of the principal reactive antigens was not elucidated. These serological investigations lend strong support to the pathogenic role and significance of P. indolicus in mixed infections with Corynebacterium pyogenes in the aetiology of heifer and dry cow mastitis.