Clinical Mastitis: The Five-minute Microbiology Lesson

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It’s the age-old question: Does this cow need antibiotics for mastitis? You don’t need a crystal ball—the answer may lie in an on-farm culture. On-farm cultures can often identify the presence of infection and the type of bacteria causing the infection and help your veterinarian make informed treatment decisions, including whether to treat at all. Linda Tikofsky, DVM, Senior Associate Director of Cattle Professional Services--Dairy at Boehringer Ingelheim, offered some best practices at the 2018 Milk Business Conference in Las Vegas.

Step 1: Prevent, prevent prevent

“I used to tell my producers that the best prevention we have against mastitis is a shovel and a rake. Keep clean stalls and clean alleyways, and we're going to reduce our risk for mastitis,” Dr. Tikofsky says. “[If] we also use good pretreatment and pre-milking hygiene, we're going to reduce it there as well.”

Step 2: Know your biology

Dr. Tikofky serves up this five-minute microbiology lesson. ”We categorize mastitis a couple of ways--contagious or environmental. So contagious means it spreads at cow-milking time. Those bacteria live primarily in the outer environment, they live outside most of the time, bedding stalls, pastures waters.” 

There are three grades of mastitis – mild, moderate and severe. The clinical signs for gram-positive and gram-negative mastitis are very similar, Dr. Tikofsky explains, but these pathogens behave differently within the udder.

“Gram positives, without treatment may be chronic. Very often, they’re subclinical for a while before they become clinical, and we know antibiotics will make a difference in those cases,” she says. “With our gram negatives, these are usually short-term. Cows are really good at identifying those infections and self-curing. And most of the time those cows don’t need treatment.” (See Figure 1: Common Mastitis Bacteria.)


Common Mastitis Bacteria (2)

Step 3: Follow field treatment protocols

The goal of intramammary (IMM) therapy is to help eliminate bacterial infection. Frequently, Dr. Tikofsky explains, treatment begins immediately after visual detection of abnormal milk. On many farms, clinical cases are often treated for about five days, many times without the benefit of a bacterial diagnosis. This means extended IMM therapy has become the industry norm. 

“We are conditioned to treat the quarter until the milk returns to normal,” she says. “In many cases this is not prudent and judicious use of antimicrobials, because the bacteria causing the infection is often eliminated early in the process.”

Step 4: Separate infection from inflammation

The goal with mastitis is to treat the infection, not the inflammation. Dr. Tikofsky offers this example. When a cow steps on your foot, it hurts, and it might swell up, but it’s not infected. Likewise, an inflamed udder may not necessarily be infected. So remember these key points: 

• The resolution of inflammation takes time.

• There is no need to treat inflammation with a mastitis tube.

• Milk will return to normal in four to six days, whether or not you use IMM therapy.

Extended IMM therapy often gets credit for cases that would have naturally self-cured, she explains. Because bacteria peaks early in mastitis cases, the udder is inflamed long after the infection is treated. Bacteriological cure precedes clinical cure, so be patient. 

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