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Streptococcal Mastitis

Sep 12, 2016

By: Kelly Whitcomb

Streptococcus is a bacterium commonly causing mastitis in dairy cows. This organism comes in numerous species, placed into two separate categories: Streptococcus and Streptococcus agalactia (Strep ag). The larger family of Streptococcus is comprised of the majority of the bacterial species, including Streps uberis and dysgalactiae, as well as S. acidominimus, S. alactolyticus, S. canis, S. equi, S. equinus, and S. parauberis. Streptococcus agalactia (Strep ag) is the other mastitis-causing bacteria associated in its own group. Each varies slightly, which is why it’s important to understand their impact, how they thrive, treatment options and prevention.

Streptococcus agalactiae can only grow and multiply within the udder, yet for short periods of time they can survive on hands, milking equipment and the outer skin of teats. When a cow becomes infected, the source of infection is always via mechanical transfer from another cow. It is introduced to a clean herd by means of a new, infected cow or by using contaminated equipment. The greatest impact from Strep ag. is a loss of milk production, and does not usually cause life-threatening illness. These losses come from decreased milk production, increased bacterial counts and somatic cell counts, and overall decline in milk quality.

Other Streptococcus bacteria are a bit more significant due to their ability to be contracted from the environment. This means that the organisms can enter the udder from outside sources, rather than direct transfer from cow to cow. Strep bacteria are found in soils, bedding, walkways or pens, and any other surface the cow may come in contact with. This infection will present in two forms, apparent (clinical) or unapparent (subclinical), and is difficult to treat effectively during lactation. It causes a high percentage of dry cow infections, while also substantially contributing to high somatic cell counts from bulk tanks. Common signs of Strep include abnormal milk, udder swelling, heat or lumps, and occasionally the cow going off feed.

Certain conditions or situations can contribute to the spread of Strep, including overcrowding, wet or humid environments, poor ventilation of housing areas, dirty or poorly maintained stalls, recent movement of cows to a new farm, access to ponds or muddy areas, and general lack of cleanliness or sanitation. These concepts are a particular concern for dry cows and calving areas where susceptibility is higher. Milking time is also where many infections occur and are influenced by the following factors: improper vacuum levels, malfunctioning pulsators, worn inflations, liner slippage and wet milking of cows.

If Strep is found on the farm, there are a few management steps to put in place in order to minimize and treat the infection. Focus on the animals with the greatest risk, for example: dry cows, cows during calving, and recently purchased cows. Immediately clean up areas that may be a source for bacterial growth, including stalls or pens, and remove any chopped straw or fine bedding. Provide a dry environment for your herd, keep them on their feet after milking by providing fresh feed, and check to make sure there are no cows suckling on other animals.

Treatment of Strep can be done numerous ways, and should be well-executed by consulting with a veterinarian. In some instances, a “blitz therapy” is used to treat all quarters of the cow with an intramammary antibiotic tube for three milkings. These infusions have also been used prepartum on cows 7-14 days before expected calving date in order to avoid infection. The other option is to culture and treat each cow diagnosed with a Strep infection. Though a small percentage of cows are not cured, it is still economically beneficial to treat.

Prevention is always the best way to avoid infection. First, increase the cow’s ability to resist the bacteria. This is done by reducing damage to teat ends due to improper milking machine function. Living environments should be clean, comfortable and allow the cow to rest in order to minimize stress. Feeding proper nutrition will also assist in boosting the cow’s immune system. Second, keep the population of infectious bacteria low. As mentioned before, keeping living and milking environments clean and dry. Use inorganic material for bedding because it is associated with fewer pathogens, and pay attention to milking hygiene by only milking clean, dry, udders. It is also important for farmers to routinely test their bulk tanks for somatic cell count for early detection of infection in their herd. And lastly, it is vital that milking staff is thoroughly trained to prevent spread of infection and keep contagious mastitis under control.

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