Guest Contributor: Katie Nanne – Veterinary Practitioner, Clare
Sun, green lush fields and summer mastitis…
July, August and September are the months of the year we tend to enjoy the most – spring is over and summer has started. However, we are not the only ones enjoying the warmer months, the larvae of the Sheep Head fly (Hydrotoae Irritans) favour this period too, to develop into adult flies and emerge. Although other types of flies have not been ruled out, it is this particular fly which is thought to be the main mode of transmission of summer mastitis. It lives in bushes and trees and flies out to feed on cattle when wind speeds are low and when it’s dry. It usually lands on the cow’s legs, abdomen or udder. They irritate the cow and she will try to swat them away with her tail and this explains why summer mastitis is more common in the front quarters. The fly prefers to feed on damaged skin sites, like teat sores. It ingests the bacteria commonly found on these sores and regurgitates them at its next feed, thus facilitating the spread of bacteria that cause summer mastitis.
A healthy teat has a properly functioning teat canal which acts as a barrier, preventing bacteria from entering the cow. At drying off a seal should be formed in the teat canal to naturally prevent infection. It can take several weeks for this seal to close the teat canal fully, and in some instances (usually when the teat end is damaged or in poor condition) this seal does not completely form, leaving the quarter vulnerable to infection. This is why infections like summer mastitis are mostly seen in dry stock or cows in late pregnancy during summer. Sometimes it is seen in heifers or lactating animals, though in lactating animals the infection is usually prevented as bacteria are flushed out at each milking.
At least six types of organisms have been found in relation to summer mastitis, of which the main two are bacteria; Truperella pyogenes (previously known as Arcanobacter pyogenes) and Streptococcus dysgalatiae. The latter is commonly found on the teat skin, particularly when the surface integrity of the teat is compromised by chaps, cuts, machine damage, pox virus, teat hurts and flies, hence it plays a major role in summer mastitis. Truperella pyogenes is often responsible for the foul smell as it tends to form an abscess when inside the udder.
A ‘classic’ case of summer mastitis has a hot, hard and swollen quarter, often with a tense, enlarged teat. The quarter is painful and when drawn a foul smelling, thick, clotted secretion or pus comes out. Usually the cow is not sick, but she could appear lame and may even have swollen hocks. If left untreated the disease could progress with the cow developing symptoms like fever, loss of appetite; she may abort or even die. When it goes unnoticed, the cow may recover and it then only becomes apparent after calving on finding a blind teat, so prompt treatment is important.
The main bacteria involved are sensitive to penicillin, thus these types of antibiotics are often used for treatment. Seek advice from your veterinary practitioner. Frequently an abscess is present, making it difficult to cure with mastitis tubes alone. Thus treatment with a course of injectable antibiotics is indicated along with frequent stripping (at least 3 times per day). Stripping it is the best way to try and prevent ‘losing’ the quarter, although this often still happens. Stripping also helps in preventing an abscess from bursting out through the side. If this happens, flush the area with an antiseptic solution to keep the wound open for drainage.
Prevention relies on maintaining good teat condition, having a good dry cow therapy protocol including the use of sealants, fly prevention (leave tails long and clean, and use fly repellents). Where possible graze cattle in open fields on ground exposed to wind and away from bushes or trees during warm dry weather.