The FDA Bulk Milk Antibiotic Survey will have an impact on the dairy industry.
By: David R. Wolfgang, Penn State, Field Studies Director
In March 2015 the FDA released the results of the Bulk Milk Antibiotic survey that began in 2012. In a survey of milk from 1,912 herds, no samples contained residues from antibiotics that are routinely tested under the Pasteurized Milk Ordinance. However, 15 samples contained residues of other antibiotics that are not routinely measured. In light of the results of this survey, producers and veterinarians should review their treatment protocols and withholding times to further reduce the possibility of residues in milk leaving the farm.
In 2010 the FDA announced that it planned to test two groups of dairy herds for additional drug residues in raw bulk milk. The FDA decided to test bulk milk for a diverse array of therapeutic products based on a high number of residues found in market animals that originated from dairy farms. These tests actually began in 2012. One group of herds selected for additional tests had a history of residues in at least two cull animals in the past year. An equivalent number of herds that did not have residue violations would serve as a control group.
The percentages vary a little year to year, but beef from dairy cattle typically averages between 8 and 16% of beef produced in the US. According to recent National Agricultural Statistical Survey (NASS) and USDA/Animal Plant Health Inspection Service (APHIS) data a substantial majority of positive residues from all meat species (i.e., fed beef, swine, and poultry) originates in cull dairy cattle. Approximately 85% of all residues in cattle come from animals of dairy origin (cull cows and bob veal calves). Such a high percentage of residues associated with dairy animals led the FDA to further investigate if more therapeutics should be included in bulk milk surveillance.
In March 2015 the FDA finally released the results of the Bulk Milk Antibiotic survey. The targeted group (positive residue tests in the past) was comprised of 953 herds. The control group numbered 959 herds. The bulk milk was tested for 27 different products. Most were antibiotics, but the tests also included anti-inflammatory compounds (e.g., Banamine®) and one antihistamine product. The testing strategy involved new methodology that could identify extremely small amounts of the therapeutic compounds. For approved products the FDA has established a tolerance level. Following extensive testing by the pharmaceutical company seeking to market a product, levels are calculated and validated to establish the withholding time for milk or withdrawal times for meat. Most withholding times are measured in days, while most withdrawal times are measured in weeks or months.
There was some good news in the FDA report. In the samples from all 1,912 herds, no residues were found for the antibiotics routinely tested under regulation established by the Pasteurized Milk Ordinance. A total of 16 residues were found in the 1,912 herds (0.78%). Eleven residues were found in the targeted herds (11 out of 953 or 1.15%; one herd had 2 different products in one sample), and 4 residues were found in the control herds (4 out of 959 or 0.42%). There was a slight increase in the number of residues in the targeted herds.
- 99.2% residue free; screened for 27 compounds (unapproved compounds at 1 ppb)
- 16 positive drug residues
- 14 of the residues detected were for drugs that have no established tolerance or safe level (presence is a violation)
- Florfenicol (Nuflor®) accounted for 10 of the 16 residues
- Ciprofloxacin (enrofloxacin-Baytril®) (1), Sulfamethazine (1) - both considered illegal
- Tilmicosin (Micotil®) (1), Tulathromycin (Draxxin®) (2), and Gentamicin (1)
- Statistically, violations not different between the two groups
Many producers have wondered why so many residues showed up when routine surveillance appeared to indicate no violations. First, it is important for producers to remember that for unapproved products there is no established tolerance level. In this survey FDA used liquid chromatography, which could find levels of chemicals much lower than in previous surveillance surveys (as little as 1 ppb). On-farm tests or screening tests at co-ops are not designed to find residues at such low levels. Second, many of the antibiotics detected belong to classes that are not normally in PMO residue tests. Since most antibiotics used on dairy farms are related to mastitis therapy, milk screening tests primarily detect the antibiotic classes used in mastitis therapy. In the bulk milk survey residues were detected for antibiotics most commonly used for pneumonia. Third, normally milk withholding times (e.g., several days) are much shorter than meat withdrawal times (e.g., weeks or months). Reviewing the pharmacodynamics (rate at which therapeutic products move around the body and then are excreted by liver or kidney) for non-approved antibiotics such as those used for pneumonia, it could be predicted that to achieve a milk level less than 1 ppb, the milk withholding might need to be several weeks longer than published meat withdrawal times. In light of the results of this survey and implications for some antibiotics, producers and veterinarians will have to review guidelines for length of withholding in cattle, even bred heifers before they enter the milking string.
The FDA has summarized their next steps following the release of this survey:
- Best management practices and education programs to reduce residues will be started with regulatory officials and milk cooperatives
- More testing will be implemented for more diverse classes of chemicals
- Along with state regulatory officials, more effort will be made to investigate and reduce residues in tissues of market cattle
Producers are encouraged to review their current treatment protocols with their veterinarian.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Extension is implied.