A Study of the Aetiology of Summer Mastitis using Experimental Infections

Abstract

A number of bacterial species are commonly associated with summer mastitis, such as Corynebacterium pyogenes, Peptococcus indolicus and Fusobacterium necrophorum. In order to study the aetiology of this disease 16 dry heifers were inoculated via the teat canal with monocultures and various combinations of these three species. Combinations of Corynebacterium pyogenes and Peptococcus indolicus, with or without Fusobacterium necrophorum, and the combination Peptococcus indolicus with Fusobacterium necrophorum resulted in a clinically acute purulent mastitis, typical for summer mastitis. All infected quarters yielded positive isolations within 5 days of infusion.

Inocula with bacterial numbers of circ. 6 x 10⁸ C.F.U. of Corynebacterium pyogenes and Peptococcus indolicus resulted in the typical clinical symptoms within 24 hours, positive isolations within 3 days and the typical summer mastitis secretion 5 days after inoculation. Serum iron, zinc and haematological values were measured at four hour intervals after experimental infection. Serum iron showed an average decrease from 27 μmol/L to 13 μmol/L, and serum zinc from 15 μmol/L to 11 μmol/L 24 hours after inoculation. Neutrophil granulocytes rose from values averaging 2.93 x 10⁹/L to 6.94 x 10⁹/L. These animals showed fever. Similar results were obtained with the group inoculated with all three species.

The observed changes in trace metals, neutrophils and body temperature are characteristic for an early host response to infection, probably mediated by members of the interleukine-1 family.