December 2014

DHI NEWSMichigan • Wisconsin • Indiana • Ohio

“Enhancing producer profitability through integrated services.”

Mastitis PCR & Traditional CultureNot ‘Apples to Apples’

~ Bridgette Voisinet, AntelBio Commercial Testing Manager & Todd Byrem, Ph.D

Like the old adage about apples and oranges, some things just can’t be considered ‘equal’.

Certainly there are similarities, but there are also some fundamental differences. Likewise, mastitis PCR should not be considered equivalent to culture. It follows then that the expectation that results from the two types of tests should be directly comparable are unreasonable. To utilize PCR, instead of establishing culture as a ‘standard’ or focusing on why culture and PCR results differ, PCR should be evaluated on the knowledge it contributes. Mastitis PCR tells you what organisms are present in a milk sample, and how much is there; a snapshot of organisms present in the milk sample. Culture tells you what organisms in the milk sample were able to grow during culture; a snapshot of the most viable organisms after a day or two of growth.

Both can readily diagnose causes of mastitis, but clearly are not the same test and will not necessarily provide the same results! While it’s tempting to revert back to what’s more familiar, and wonder what results culture would have returned, don’t shortchange the value of the information provided by PCR!

Let’s work through a scenario. You take an opportunity to have your DHI

specialist submit samples for mastitis PCR testing. Mastitis PCR identifies A LOT of Staph aureus in A LOT of your high SCC DHI samples. Now what? Management’s focus should be on controlling contagious mastitis and in particular, identifying and eliminating sources of Staph aureus. Efforts should be made to change procedures to effectively reduce transmission, limiting new infections. Once practices have been implemented, target follow-up PCR testing on high SCC samples. Success would be reducing the number of Staph aureus cases on a subsequent test-day.

Could you accomplish success by using culture in the case above? Most likely. Despite the fact that results from cultures of hand-stripped samples from the same cows would be somewhat different, they would most likely yield a similar conclusion. It’s important to remember then, that mastitis PCR on DHI samples is faster (providing results by the time cows could even be stripped for culturing), more sensitive (identifying more infected cows), and

certainly more convenient (no hand-stripping or shipping samples)!

To reinforce the point, consider a real-life example. A herd observed an increase in mastitis, and tested cows from their hospital pen. Nineteen of the cows tested positive for Mycoplasma by mastitis PCR. When hand-stripped samples from the same cows were sent for culture a couple days later, only 12 were positive for Mycoplasma. Different results, but the same conclusion. No mistake about it, the original mastitis PCR results indicated an outbreak

of ycoplasma, and called for a plan to control and eliminate new infections. Add the culture results to the equation, and one may be inclined to put the seven culture negative cows back in the milking string, but considering the enhanced sensitivity of mastitis

PCR, this could prove to be costly!

A well-planned and executed mastitis program is critical to controlling mastitis. While it’s tempting to give more regard to an old comfortable standby, consider the value PCR information provides, as well as the convenience. Contact us at 800.631.3510 to discuss how mastitis PCR can help with your mastitis control program.

“Mastitis PCR on DHI samples is faster,

more sensitive and more convenient

than culture.”

NorthStar Cooperative: 1.800.631.3510 • Michigan ULS Lab: 1.800.836.8114 • Wisconsin Lab: 1.800.436.9344 • northstarcooperative.com

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