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Drug Residue Screening Tests

Dairy Pipeline: April 1998

by G. M. Jones, Extension Dairy Scientist
Extension Dairy Scientist, Milk Quality and Milking Management
Virginia Tech
(540) 231-4764 email:

If you are using a drug residue screening test for milk, make sure it will detect drugs you use. You need to understand which drugs specific tests will and will not detect. On-farm screening tests may not detect all antibiotics in milk that are used on your farm. For example, if the Delvotest detects only penicillin, cephapirin, ceftiofur, ampicillin, and amoxicillin, and you use novobiocin, the milk sample will test negative but it may not be negative if the milk plant uses Charm II which can detect novobiocin and many other drugs at violative levels. It's a good idea to test milk from treated cows at the end of the milk discard time but make sure that you use a test that will detect the drug in question. Many screening tests are unable to detect oxytetracycline, erythromycin, sulfa drugs, novobiocin, polymixin B, and others. Read the directions with the test or consult your veterinarian. Don't put yourself into a sense of false security. Use the dosage recommended with the treatment or recommended by your veterinarian and discard milk according to directions.

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