Field Trial Demonstrates Accuracy of Mastitis Test

4/20/2013 7:00 AM

DURHAM, N.C. — A new, on-farm test that identifies subclinical mastitis in individual udder quarters will enable dairy producers to selectively treat cows at dry-off and reduce treatment costs.

The test, to be marketed as Qscout MLD, identifies, differentiates and counts three primary leukocytes (white blood cells) in milk. Known among scientists as the milk leukocyte differential (MLD), the test automatically assesses the information and indicates whether subclinical mastitis is present before symptoms are even visible to the producer. The test is modeled after the blood leukocyte differential, which has been used in humans and companion animals for decades to reliably detect infection, even in the early stages.

A recent field trial demonstrates that when the new test is used for diagnosis, selectively treating only cows that test positive for infection is as effective as blanket treatment — the standard industry practice of administering antibiotics to all cows at dry-off, regardless of disease status.

“Selective dry-cow therapy has been shown to have economic benefits, but it hasn’t been a practical option because currently available testing methods are either costly and time-consuming or they lack accuracy,” explained Mitchell Hockett, Ph.D., director of technical research for Advanced Animal Diagnostics (AAD) and the principal investigator of the study.


The trial results were presented recently during a forum hosted by AAD, the test’s developer, at the National Mastitis Council’s annual meeting in San Diego, Calif.

Quarter milk samples were collected within 24 hours of dry-off from 300 Holstein cows that were around 223 days in gestation. Investigators then screened the samples using the MLD; they also obtained somatic cell counts and bacterial cultures.

Half the cows in the study were randomly assigned to a traditional treatment group and had all four quarters dry-treated with the antibiotic cephapirin benzathine. The remaining cows were assigned to a selective group, and only those that tested positive for subclinical mastitis in at least one quarter were treated in all four quarters. All cows in the study then had their teats sealed with an internal sealant and treated with a barrier dip.

Ten days after calving, investigators collected quarter milk samples for culture.


At 24 hours prior to dry-off and 10 days after calving, the rate of quarter-level infection as determined by culture did not differ significantly between the traditional and selective groups. On day 10, the rate of infection was numerically lower in the selective group.

“We undertook this dry-cow study to put our MLD technology to a tough test,” said Joy Parr Drach, AAD’s president and CEO. “Untreated subclinical disease at dry-off puts a cow at significantly higher risk for developing clinical mastitis later on, so accurate diagnosis is essential to successful selective treatment.”

She added, “The results of this study reinforce the diagnostic accuracy of the MLD. It shows that Qscout MLD can help producers use antibiotics judiciously at this critical stage of lactation — and realize the economic benefits of selective treatment — without increasing infection rates post-calving.”

The Qscout MLD test equipment consists of a reusable milk collection device, a disposable diagnostic slide and a reader, which is a fluorescent imaging system housed in a tabletop unit that requires less space than a traditional computer. Units are expected to become available later this year and will be marketed to producers and veterinarians. Use of the test requires some basic training but does not require skilled personnel.

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