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Can You Visibly Detect Contagious Mastitis in Your Herd?

05 September 2018

Contagious mastitis is often subclinical, so it's very difficult to detect with the naked eye, says Dr. John Middleton, professor at the University of Missouri, during an interview at the international meeting for the National Mastitis Council held in Milano, Italy in June.

Usually a producer or veterinarian will need to use some indirect measure to identify when a cow has mastitis. For example, using a California mastitis test to detect an elevation in somatic cell count.

"But the thing about using the California mastitis test or an elevation in somatic cell count is: it doesn't tell us what bacteria is present. So, we could have sub-clinical mastitis with bacteria that leave the mammary gland quite quickly, and therefore don't present a long-term problem for the cow or for the herd," said Dr. Middleton.

"If we're dealing with something like Staph aureus or Strep agalactiae - possibly mycoplasma - some of those organisms that can be subclinical and get into the mammary gland, they can stay there for a very long time and they present a reservoir for other cows in the herd and generally transmission occurs at the time of milking."

Value of Identifying Mastitis Bacteria

It's very helpful if producers can identify the mastitis-causing bacteria. It can then be determined if it will pass from cow-to-cow, he said. Ideally, the next step is to manage the cow so that she doesn't spread bacteria to other animals.

Conventionally, that's been done with routine culture. In the case of a slow spreading subclinical infection, culture may be a reasonable option, but there are systems where culture-independent methods are needed to more rapidly detect the bacteria. For example, in automated milking systems where individual cow samples aren't taken, there might be opportunities to do culture-independent types and techniques in the future where we can detect contagious pathogens at the time of milking.

"Culture-independent techniques, such as PCR, can also be used to diagnose the bacteria that are in the mammary gland. We can use culture-independent techniques on the mammary quarter level. We can use those at the cow level, and we can use those at the bulk tank level," Dr. Middleton noted.

"At the bulk tank level, we're doing a very crude screening of the population of cows to say, are there contagious pathogens in this population of cows. We can keep measure of − are there Staph aureus cows in this herd, are there Strep ag cows in this herd, are there Mycoplasma bovis cows in this herd. Once we figure out whether we're finding contagious pathogens, we can mine down to the cow level or even the mammary quarter level to look at which cows are contributing those contagious pathogens to the bulk tank."

An advantage to using a culture-independent technique is that if a producer or veterinarian is only screening for contagious pathogens at the bulk tank level, samples can be collected as part of a producer's routine monitoring system. If pathogens are found, then the producer and/or veterinarian know they need to look more closely at the rest of the cows in the herd to make a diagnosis.

Multiple Options for Diagnosis

"Initially we might detect the inflammation, so that would be California mastitis test or somatic cell count," he said. "We would then want to know, do we have contagious pathogens that are causing that elevation in bulk tank somatic cell count."

From there, producers and veterinarians determine if contagious pathogens are present at the bulk tank level. Next Dr. Middleton said to drill down and figure out which cows have those contagious pathogens in order to control the spread of disease. This can be done either with conventional culture or with PCR.

"The reason that culture-independent PCR-based techniques probably work well for us for contagious pathogens is that the contagious pathogens typically are harbored by the cow. And so if it's in the milk of that cow, it probably means that the cow is in fact a reservoir," Dr. Middleton explained.

For contagious pathogens, it's therefore possible to screen at much higher levels like the bulk tank milk. So culture-independent techniques on bulk tank type samples for contagious pathogens are very practical.

"When we start looking at bugs that can be found in the environment as well as in cows, that's a little bit trickier to determine if it's in the bulk tank, did it get there because we've got dirty teats, because we've got street canal colonization, have we got dirty equipment?" he said. "Whereas for contagious pathogens, because we think generally they come from inside the mammary gland, screening of the bulk tank level for those bugs is quite relevant to what we're trying to do to control mastitis."

For more information about cattle diagnostics, click here or connect to the Thermo Fisher Scientific Cattle Resource Center.

 

Sarah Mikesell, Senior Editor

Sarah Mikesell, Senior Editor



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