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When you’re sick, your doctor usually runs a test or two to determine which bug is making you ill. From these results, he plans an appropriate treatment strategy that may or may not include antibiotics, depending on the source of the ailment.

That same strategy works well for managing your herd’s udder health.

New on-farm research from Michigan State University, presented recently at the National Mastitis Council’s annual meeting, shows that a mastitis treatment protocol based on milk culture results — not on intuition or experience — can significantly reduce mastitis treatment cost and milk-withholding times. In this study, the number of clinical cases that required intramammary antibiotics dropped by 80 percent, reports Phil Sears, Michigan State University dairy veterinarian.

Results like that can quickly add up. For example, let’s say treatment cost on your dairy is $5 per infected quarter (not including lost revenue from discarded milk), and your cows average 500 infected quarters a year. If you also discover that 80 percent of clinical cases do not warrant medication based on culture results, you can save $2,000 in treatment cost alone just by knowing which pathogen infects your herd ($5 X 500 = $2,500 X 0.80 =  $2,000 less than the total cost of treating all quarters).

Culture all cases
Using animals from a 3,200-cow dairy, Michigan State researchers cultured the milk from every cow that entered the mastitis pen. Cows entered this pen when the herd manager determined that the animals showed signs of clinical mastitis, like abnormal milk.

Only milk from infected quarters was cultured, and all streptococcal organisms were further tested to determine the presence of Strep. agalactiae. The presence of Staph. aureus also was sought through cultures, though no cases were found.

In the study, cows in the mastitis pen were not treated until culture results were received. This is a marked difference from treating every clinical case as soon as it is detected.

If E. coli or Klebsiella appeared in cultures, the cow was not treated, but the quarter was monitored. All other infected cows were treated to evaluate the effectiveness — or ineffectiveness — of extensive antibiotic treatment, regardless of infection source.

Strategy gets results
Researchers compared how long it took treated and untreated cows to return to normal milk, when in lactation mastitis infections occurred, and how many quarters were lost to infection.

Here is what they found.

  • Most clinical cases occurred in the first 100 days of lactation.
  • Infections peaked at 25 days and 75 days of lactation for gram-negative bacterial infections, like E. coli. Twenty-eight percent of gram-positive infections — caused by various species of Staph. and Strep. — were cultured in the first 25 days of lactation.
  • Intramammary antibiotic use dropped 80 percent when treatment was limited to cows that had quarters that cultured positive for gram-positive bacteria.

That’s because 55 percent of the clinical cases cultured in the study resulted in “no-growth” cultures — that is, the sample did not grow bacteria in the lab, making it impossible to know which treatment to use. And, 25 percent of the cases cultured gram-negative bacteria that did not require antibiotic treatment. Herd managers couldn’t know this status without testing their milk samples.

Therefore, if this herd had not followed a culturing protocol, managers would have treated most of their herd’s mastitis cases unnecessarily.

  • When treatment was withheld for 24 hours pending culture results, most of the clinical signs resolved themselves.
  • Milk from cows in the “no-growth” category that received antibiotic treatment did not return to normal milk quicker than cows in the category that did not receive antibiotic treatment
  • Cows in the “no-growth” category that received antibiotic treatment did not have fewer lost quarters than cows that did not receive treatment.

In fact, this “no-growth” category was discontinued before the end of the study because response to no treatment was just as effective as antibiotic treatment. Additionally, cows were back in the milk string earlier since they were no longer subjected to milk withholding due to the use of antibiotics. Also, treatment did not decrease the time it took for milk to return to normal because it had no impact on the afflicting infection.

Sticking with the program
After the study was completed, the cooperating dairy elected to continue the culture protocol. Currently, cows with clinical mastitis are cultured and monitored for fever, as demonstrated by the decision chart on page 70. Cows do not receive antibiotic treatment unless test results indicate streptococcal and staphylococcal intramammary infections. Cows return to their herd-mates when milk becomes normal in appearance.

Ultimately, this change in treatment protocol increased mastitis monitoring in the test herd, reduced the number of days of lost production, and decreased the amount of antibiotics used.