Violative residues: A dirty word

Residues. What do you think about when you hear this word? Residue prevention, antibiotics, farms, veterinarians, meat, milk, food — all are applicable. All domestic and imported food products are tested for residues through the National Residue Program, which is administered by the U.S. Department of Agriculture Food Safety and Inspection Service. Meat, poultry, egg products and fish products are required to meet specific standards established by the Food and Drug Administration and the Environmental Protection Agency. These standards ensure that food products comply with U.S. requirements for veterinary drug, pesticide and chemical contaminants.

Based on a semi-recent experience with residues at slaughter, I would like to share some applicable information that I learned.

First, carcasses are checked on the floor with a preliminary test. This can be random surveillance or inspector-generated. Surveillance sampling is scheduled testing performed on random carcasses after they have passed antemortem inspection. Inspector-generated sampling is conducted when FSIS inspectors suspect animals have potentially violative residues. This may be based on a producer’s history of violative residues, the individual animals exhibiting signs of systemic disease or the animals that have injection site lesions.

When an animal carcass is tested, the public health veterinarian uses a KIS, or kidney inhibition swab test. This test is positive or negative but does not specify which drug the animal is positive for. The carcass is retained until results are returned. Further samples are collected if an animal tests positive on the preliminary test to determine the type of drug and the level present. Occasionally, carcasses are retained even if KIS is negative if other chemical residues are suspected. The public health veterinarian is responsible for condemning carcasses and parts of animals found to have violative residues.

Additionally, the positive residue results are published for public review in the FSIS annual sampling report each year. The names of violators with two or more violations in 12 months are posted on a USDA repeat violators list that can be used as a reference by meat processors and livestock markets to determine if purchased animals are at high risk for residues.

Where do the withdrawal times come from? The FDA establishes the period after drug treatment when milk and eggs are not to be used for food and during which animals are not to be slaughtered. This allows the animals time to eliminate the drug residues. However, there are times these withdrawals might be inadequate depending on the severity of the animal’s condition. To make this more confusing, some products approved for use have a tolerance level. If the animal tests below the level, it is OK for human consumption, but some products have a zero-tolerance level if they are not approved for the class of animals. Such an example would be Nuflor (florfenicol). While it has an approved label for calves and beef cows, it does not have an approved label for dairy cattle over the age of 20 months. This means there is a zero tolerance for levels of florfenicol in milk and slaughtered dairy cows (lactating or dry).

How do you know which withdrawal to use? Product labels are required to have withdrawal labels when marketed. Additionally, if a veterinarian has prescribed a product in a way that does not match the published label, the veterinarian should label the product with new directions, the appropriate withdrawals, and provide written treatment protocols with clear directions as well. Another helpful resource is the Food Animal Residue Avoidance Databank, called FARAD. FARAD is a directory of residue avoidance information and has an excellent website where questions can be asked for specific withdrawals.

What are the most common causes of residues? Dairy cows, beef cows and bob veal made up the bulk of violative residues in 2023 (2024 is not published yet). The chemical residues varied, but ampicillin, desfuroylceftiofur (ceftiofur), flunixin, penicillin and sulfadimethoxine were most frequent. These products have labels for dairy cows and were likely the result of incorrect dosage, administration or not waiting long enough before selling to slaughter.

Several more chemical residues in dairy cows also caught my eye. Some dairy cows tested positive for gentamycin sulfate, doxycycline and dihydrostreptomycin. Quite frankly, these drugs have no business being used in cattle at all: beef, dairy or other. They have no label or evidence to support their use and no appropriate withdrawal period to follow.

Consider the following when reviewing residue risk on your own farm. Do the following items occur?

— Treated cows are not recorded or identified, which results in treated cows being milked into the bulk tank or being sold for slaughter.

— Dry cow tube withdrawals are not observed. Make sure to follow all withdrawal periods for both milk and slaughter, especially if the cow calves early.

— Drugs are used illegally or incorrectly. An example is using Nuflor in a dairy cow or giving Excede in the tailhead or in the neck instead of the proper base of ear location.

— Cows are treated for extended periods, but the withdrawals are not extended to compensate. If you extend treatment even by accident, extend your withdrawal. Ask your veterinarian or use FARAD to help determine an appropriate holding time.

— Remember, withdrawal periods are established using studies from healthy cows. The reason being that the physiology of a healthy cow is more consistent and better understood. Therefore, sick cows may require extended withdrawals due to dehydration and impaired kidney and liver metabolism.

— Perhaps another question should be considered: Is it worth treating the cow? Does she have a chance of recovery with treatment, or is she better off being destined for slaughter or euthanasia? Dry cow treatment could be included in this as well. Can your farm manage the residue risk associated with dry cow antibiotics?

Megan Weisenbeck is one of six veterinarians at Northern Valley Livestock Services in Plainview, Minnesota. She practices primarily dairy production medicine in Minnesota and Wisconsin. Megan can be reached at [email protected].