Summer Mastitis

As its name suggests, summer mastitis is a type of mastitis which occurs predominately during the warmer summer months. It is a condition affecting the non-lactating animals, particularly dry cows and heifers at pasture, but can even occasionally occur in calves and bulls. It is estimated that up to 60% of herds in the UK are likely to experience summer mastitis each year. If left untreated the infection can permanently damage the quarter and even lead to abortions and deaths. Very few quarters recover, so efforts should be made to reduce incidence or avoid the disease completely.


Summer mastitis is an infection which is caused by a number of bacteria which are found normally in the environment. These gain entry to the udder resulting in mastitis. The main causal bacterium is Trueperella pyogenes but other bacteria can exacerbate the disease. It is more commonly found in farms and even certain fields within farms where flies are common suggesting that this is the cause of spread.

The seasonality is also related to the time of year when the sheep head fly Hydrotaea irritans is most active. These flies are believed to be a means of bacterial transmission. Their habitat is around trees or bushes, damp ground and stagnant water.


In obvious cases the infection causes the udder to become swollen and hard. The affected animal is easily identified as it often stands alone away from the herd, is dull and inappetent. This is an extremely painful condition meaning the affected animal is reluctant to keep pace with the other animals, may be stiff and lame when moved. On examination the temperature is often high and the quarter affected contains thick foul smelling pus.

These obvious signs do not occur in every case and it is suggested that when a blind quarter is discovered after calving that these animals may have had a mild infection without showing any significant clinical signs.

Treatment & Control

Treatment is most often via regular and repeated stripping of the affected quarter, to remove as much affected material as possible, followed by intra-mammary antibiotics and an antibiotic injection to counter the systemic effects of bacterial toxins. Heifers and cows with summer mastitis are best isolated to prevent the spread of the illness.

Summer mastitis can be avoided by various measures:

  • Having effective dry cow therapy, including the use of long-term intra-mammary antibiotics, teat end sealants and good hygiene measures at drying-off. In some circumstances, intra-mammary antibiotics may require re-administration during the dry period, although care should be taken with milk withdrawal periods.
  • Implementing measures to control and minimise exposure to flies. Flying insects should be controlled from early on in the fly season by the use of pour-on anti-parasitic treatments, the use of fly ear tags, and the application of teat fly repellents to teats, such as traditional Stockholm tar and brown salves.
  • Maintaining good teat condition pre-drying off, having good dry cow nutrition and observing/checking cattle on a regular basis.
  • Avoiding areas where teats may be damaged or areas where flies are a particular problem, such as near rivers and woods.

Reference: Dairy Co & Farming Life