Prevention’s the best policy for summer mastitis

By Seán Doorley, beef & sheep adviser, Longford Town

The incidence of summer mastitis tends to vary from year-to-year, with it being a particular problem in many herds this year because of the dry weather.

It occurs mainly in the June-to-September period, affecting dry cows and in-calf heifers when fly numbers are highest. In reality, however, it can occur at any time of year.


The primary causal organism is Actinomyces pyogenes in conjunction with other organisms that either enhance its activity or allow infection to develop.

It is a very severe form of mastitis causing udder damage, high temperature and toxaemia. Infected quarters are generally lost and treatment is focused on saving the animal and preventing pregnancy loss.

The infected quarter becomes swollen and hard. When the quarter is drawn, the strippings will be foul smelling. The extract may appear clear or with soft-to-cheesy type curds and, as damage progresses, there may be traces of blood.


Where possible, prevention is the preferred policy. There are several areas of prevention to consider.

1. Fly control

A number of pour-on products are available to control flies. They are based on synthetic pyrethroids such as permethrin and deltamethrin.

It is recommended to apply these along the back of the animal, but is probably no harm to direct some around the udder area as well.

A number of these products will give cover for four weeks; but – in a year when the incidence of summer mastitis is high – it should be applied every two weeks.

Ear tags containing cypermethrin are also available for fly control. Other farms have been applying stockholm tar on the udders of susceptible animals. Although it will deter flies, it is messy and may need to be applied every four-to-seven days.

2. Grazing conditions

Where animals are let graze during the dry period may have a bearing on the level of flies. It is advisable to avoid fields that are well sheltered with a lot of tree cover.

Try and keep the fields topped to reduce tall weeds or old senescent seed heads, which can provide cover for flies or can aid in the spread of infection as animals walk around the area.

3. Teat damage

Animals with any teat soars should be housed. Soars will only attract flies and increase the likelihood of infection.

4. Isolation of infected animals

Animals showing signs of infection should be removed from the group and kept isolated. If the infected quarter is milked out, the strippings should be carefully discarded because of the risk of spreading infection.

In all cases, consult your vet for advise on prevention and treatment of summer mastitis in your herd.