Summer mastitis or August bag

Farm vet Sandy Jamieson discusses summer mastitis. Detailing the causes, treatment plans and preventative measures.

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Summer mastitis or August bag

The name gives a big clue to this condition. This is a potentially devastating mastitis, predominantly seen in dry cows and in-calf heifers (but can affect any animal; beef cows not just dairy, and also bulls/bullocks/calves) during the summer. By the time the animal is picked out the quarter is normally beyond repair and treatment is for salvage. Also, because of the fever and toxins involved, there is a significant risk of the animal aborting.


The bacteria involved are Trueperella pyogenes, Peptostreptococcus indolicus and Strep. dysgalactiae. The condition may start from teat sores but the head fly is heavily involved in its spread, hence its occurrence predominantly in July, August and September when head flies have hatched and are on the wing.

The flies like damp, humid conditions and low wind speeds which means certain fields will pose a higher risk (ponds and woods). The affected animal is often dull, slow to move and may appear lame. On closer inspection one quarter (or more) will be obviously enlarged with the teat swollen.

The animal is normally pyrexic with a temperature of 104 or more. The teat will be hot and sore to the touch (good way to get kicked). When drawn the pus is like a yellow/green thick rice pudding with a really foul smell (you wouldn’t eat much of it).


Treatment will normally save the animal but unless caught very, very early the quarter is unlikely to recover. Antibiotics by injection (Pen-strep/Betamox/Synulox) along with nonsteroidal anti-inflammatories (Finadyne/Ketofen/Metacam) should be administered and the quarter stripped as often as possible (the strippings should not go onto the ground as they are a source of further spread; dispose of using plenty of disinfectant).

Intramammary preparations can be used but the pus is often so thick it is difficult to imagine how useful they will be. Treatment should be kept up for a minimum of 4 days and potentially 7 days. People will often say that the quarter will only clear up once it actually bursts like an abscess which is why older treatments have involved splitting the teat top-to-bottom to facilitate drainage (this does carry a risk of haemorrhage!).


Prevention is therefore the most important thing to concentrate on.

  • Stockholm tar applied to the teats was the original favourite but is really messy and needs done very regularly (looks really bad on your sandwiches).
  • Fly prevention using either tags or permethrin pour-ons is definitely easier and for peak periods a small amount of pour-on can be directly smeared on the udder.
  • Antibiotic dry cow tubes and teat sealants are also effective but are difficult to use successfully in heifers and beef cows, but in conjunction with fly control would be gold standard.
  • If it’s a recurring loss on a certain farm then calving policy may have to be changed so that animals are calved before the risk period

Of course, if you have any concerns, don’t hesitate to contact the team.

Header image: Hydrotaea irritans.Photo by Gail Hampshire, reproduced under the Creative Commons Attribution 2.0 Generic license.

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