Test the tank, not the cow
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Test the tank, not the cow

July 25, 2016
POSTED BY: Gary Neubauer | DVM | Senior Manager | Dairy Technical Services | Zoetis

You recently treated your dairy cow with antibiotics for a case of mastitis. Assuming you worked with your veterinarian to determine the pathogen and appropriate treatment, and considering you followed the antibiotic’s label directions for dose and proper route of administration and milk withhold time, her milk should be ready for the bulk tank again. But how can you be sure?

I work with many producers who think the best way to prevent violative drug residues in milk after mastitis treatment is to test the milk from the individual cow to ensure a completely unadulterated product. Unfortunately, it is not that simple. Research has shown that testing individual cows instead of testing the bulk tank, can create false positives and cost dairies money, in terms of added days in milk withhold.1 In this case, it’s important to note that cows individually tested have been treated according to approved label directions for lactating cows. Testing individual cows is always necessary for cows being treated in an extra-label fashion.

The problem with individual cow testing
The problem with testing individual cows (treated according to approved label directions) is that none of the 16 Food and Drug Administration (FDA) accepted assays to screen milk for beta-lactam drugs were evaluated for use on individual cows. While none of the tests for beta-lactam drugs appear to produce a negative result on an antibiotic-spiked milk sample, many produce false positives and false violative results when  milk samples are tested from individual cows.1 A false positive or false violative result causes the producer to throw away perfectly salable milk.

If the products are used extra-label, or combinations of two or more products are used, you could be at risk for a residue violation. The milk from those individual cows should be tested if appropriate tests for those specific drugs are available. Nevertheless, the label discard times for approved products used according to label are much more accurate than the currently available FDA tests.

The FDA imposes tremendous scrutiny on the manufacturers of animal health pharmaceuticals. Approved antibiotics, when used according to label, have the backing of both the manufacturer and the FDA. There is more science behind the label directions and withdrawal times of approved dairy antibiotics than there is in the current validation of antibiotic assays.

Consider testing the bulk tank
Producers should consider testing every bulk tank of milk before it is shipped with the same or equivalent assay used by the milk processor. Compared with the several thousand dollars a producer would lose paying for a tanker, the $500 to $800 a year that it would cost most dairies to test every bulk tank is a minimal and worthwhile investment.2

Always consult with your veterinarian about implementing a mastitis prevention plan and mastitis treatment plan based on common pathogens on your dairy operation to provide the best chance for a complete bacteriological cure.  For a mastitis treatment that can provide broad-spectrum coverage and help achieve a bacteriological cure against leading mastitis-causing pathogens, talk to your veterinarian about SPECTRAMAST® LC (ceftiofur hydrochloride) Sterile Suspension. In addition to having a low residue profile, SPECTRAMAST LC has a shorter milk withdrawal time of 72 hours compared with competitor products, like ToDAY®.

IMPORTANT DIAGNOSTIC INFORMATION: SPECTRAMAST LC is intended for use in lactating dairy cattle only with the specified, labeled pathogens. To assure responsible antimicrobial drug use, it is expected that subclinical mastitis will be diagnosed using a positive culture, or other pathogen-specific test, in addition to any other, appropriate veterinary medical evaluation prior to treatment.

IMPORTANT SAFETY INFORMATION: People with known hypersensitivity to penicillins or cephalosporins should avoid exposure to SPECTRAMAST LC. Product requires a 72-hour milk discard period and a 2-day pre-slaughter withdrawal period following the last treatment. Use of this product in a manner other than indicated on the label, or failure to adhere to proper milk discard period, will result in violative residues. See full Prescribing Information.


1 Cullor JS. Dilemmas Associated with Antibiotic Residue Testing in Milk: Choices, Problems, Issues. In: Moats WA, Medina MB, ed. Veterinary Drug Residues, Food Safety. Washington, DC: American Chemical Society; 1996.

2 Neubauer GD. Antibiotic Residues: Perception vs. Reality. http://purl.umn.edu/118823. Published May 22, 1996. Accessed June 9, 2016.



  • Manage milk quality for better repro, more milk
  • Carefully follow and understand label directions
  • Demystifying mastitis treatment


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