Summer mastitis affects dry cows and heifers during the summer months, with it usually being seen from late-June to mid-September.

It is most commonly seen in these months as it is when fly numbers are highest – however it can occur at any time of the year.

Summer mastitis

Summer mastitis is caused by the organism Actinomyces pyogenes, along with a number of other organisms that either enhance its activity or allow infection to develop.

This form of mastitis is very severe and causes udder damage, high temperatures and toxaemia.

The infected quarter becomes swollen and hard, and when stripped it will be foul smelling.

The extract may appear clear or with soft to cheese-like curds and as damage progresses there may be traces of blood.

An infected quarter is generally lost and treatment is focussed at saving the animal and preventing pregnancy loss.


There are a number of ways to prevent cows and heifers from picking up summer mastitis.

Some fields, usually those with a large amount of trees or tall weeds, are more likely to lead to infection than others. The trees and weeds can provide cover for flies and thus increase the likelihood of an animal picking up an infection.

For fly control, the use of pour on or other products should be used to control numbers near or around stock.

These products should be used as instructed to ensure maximum effectiveness.

On some farms, Stockholm tar is used around the teats to prevent infections, particularly in heifers.

One of the major drawbacks of using Stockholm tar however, is that it must be applied to the udder at least once a week.

With that said, it does offer you a chance to train heifers into the parlour if they are being kept on the home block.