The Epidemiology of Summer Mastitis

Abstract

The incidence of summer mastitis, or more accurately A. pyogenes/anaerobe mastitis, is considered in terms of animals at risk, stage of gestation, season of the year and geographical occurrence of the infection. It is significant that a large proportion of cases occur in the spring in housed animals. However the majority of cases are associated with autumn calving cows and heifers, at summer pasture.

Susceptibility to infection varies with the age of the cow, breed, breeding and husbandry. Disease is coincident with the occurrence of a potential vector, the fly Hydrotaea irritans, in summer but not in winter/spring. The mechanism of infection might be similar in both seasons once the cow is contaminated by the bacteria. The absence of the vector in spring may explain the much lower incidence of disease then.

Little is known of the effects of husbandry, especially nutritional and environmental stresses, on increasing susceptibility to infection. This should be remedied. More accurate diagnosis is required, it is at best 80% accurate, to confirm A. pyogenes/anaerobe mastitis, as anaerobic culturing is rarely used routinely.