Isabel Richards, Veterinary Science – South Africa and owner/operator of Gibraltar Farm
(Previously published with the Eastern Alliance for Production Katahdins (EAPK): May 25, 2021)
Whenever we sell animals, be it at auction, privately as feeder lambs, breeding stock or even just pets and lawnmowers it is our responsibility to make sure that the animals we are selling will not enter the food chain with illegal drug residues in their tissue. Animals that are sold at auction need to be ready to slaughter as many enter the food chain within hours or days after being sold. Private sale feeder lambs, pets and breeding stock animals can be sold before their drug withdrawal times are over as long as you tell the buyer and they are okay with taking responsibility. Be sure to include the information on the bill of sale too, for your protection. The animal you are selling might not be intended to go to slaughter any time soon, but accidents happen and circumstances change, so buyers need to be aware if the animals have drug residues in their tissue.
Animals are randomly tested for drug residues at slaughter by the food inspection service officers. Animals that test positive for violative residues are detained and reported to the FDA for enforcement action. You can learn more about the possible consequences of allowing animals with violative residues enter the food chain here.
Keeping careful records of all drug treatments, and checking them before sales, is the best way to prevent inadvertent sales of animals with violative drug residues. You can see the recommended records to keep here.
Drugs that are approved for use in food producing animals have had studies done to determine the maximum allowable drug residue in meat or milk that still makes the product safe for human consumption. Approved drugs must be used in the specific species, at the specified dose and via the route(s) of administration listed on the label for the drug withdrawal time listed on the label to apply. When you use a drug in a different species, at a different dose, or different route of administration, it is considered extra label drug use and the withdrawal time on the label no longer applies.
Under U.S. law, any extra label use of drugs (including non-prescription drugs like oxytetracycline or Safeguard, that are not labelled for sheep) should only be used after consulting with your veterinarian so that they can give you an appropriate withdrawal time. Veterinarians can submit a request to the Food Animal Residue Avoidance Database (FARAD) to supply you with a withdrawal time for extra label drug use. You can look up drug withdrawal times for some commonly used extra label applications in sheep on the FARAD webpage.
Why is the withdrawal time different if used in a species not listed on the label?
When a drug is approved for a specific species, the research has been done to see how long it takes that specific species of animal to metabolize the drug in question. Different species metabolize the same drug at different speeds so you cannot assume the same withdrawal time applies. For example, the recommended dose for procaine penicillin G (one of the few drugs labeled for sheep) has a withdrawal time in cattle of 14 days, in sheep 9 days and in pigs only 7 days. Sheep are better at metabolizing penicillin than cows, but cattle are better metabolizing other drugs than sheep, so you cannot extrapolate a withdrawal time on your own.
Why is the withdrawal time different if the drug is used at a different dose than listed on the label?
In general, we use the cattle dose when giving medications to sheep. Remember that if you give additional doses than are recommended or give a higher dose or dose more frequently than the label recommends, you will need an extended drug withdrawal time. Higher doses of drugs take longer to metabolize and if too high, can be toxic to the liver or kidneys, slowing down the metabolism even more.
For drugs that list a maximum volume (ml) of product that can be administered in one site, you will also have an extended withdrawal time if you exceed that. A bigger bolus of medication in one spot will take longer to be absorbed and therefore longer to metabolize.
For instance, Safeguard’s (Fenbendazole) drug withdrawal time for goats on the label is 6 days when used at 5mg/kg for a single dose treatment. Using the same drug to treat meningeal worm in sheep at 25mg/kg for 5 consecutive days has a significantly longer drug withdrawal time of 90 days.
Why is the drug withdrawal time different when administered by a different route than listed on the label?
Intravenous (IV) – medications administered intravascularly spread immediately throughout the animal’s body including the liver and kidneys where it is broken down and excreted out of the body. In general, drugs that are given by this route clear quickly and have shorter withdrawal times.
Intramuscular (IM) – medications administered into a muscle are absorbed at a slower rate than IV medications but faster than subcutaneous (SQ). As blood flows around this bolus of medication, it gets absorbed. It is not fully excreted from the body until the whole bolus has been absorbed.
Subcutaneous (SQ) – medications are administered under the skin into the fatty tissue. Because there are few blood vessels in the surrounding tissues, subcutaneous injections are absorbed at a slower, more sustained rate and have longer withdrawal times.
Oral (PO) – medications are administered through the mouth. Some drugs like anthelmintics work directly in the intestinal tract, while others like meloxicam need to be absorbed into the bloodstream to have their desired effect. The amount of food in the intestinal tract can greatly influence the speed of absorption. If a drug label says to withhold food for a certain period, be sure to follow the instructions for optimal effectiveness of the drug. Remember: De-wormers have drug withdrawal times too, check your labels.
If you use a drug like Banamine (Flunixin meglumine) that is labeled for IV use in cattle and give it IM, you will end up with a longer withdrawal time when compared to using it IV. Be careful if you decide to give drugs that are labelled for IV use by another route, some of these drugs can cause severe inflammation at the injection site.
Remember to look at labels for drugs that are applied topically too. They may seem safe, but many are absorbed systemically. A lot of the OTC ointments and sprays are not approved for use in food producing animals. Red-cote and Blu-cote have warnings on their label “Not for use on food producing animals”. Nitrofurazone ointment that is commonly used in horses comes with a “Caution: Federal Law Prohibits the use of this product in food producing animals.”
There are some drugs that are prohibited from extra label use. Be sure to check with your vet before using drugs intended for your dog, horse or even other food producing animals. You can find a list here.
Whenever you medicate an animal, make sure that you record it and preferably mark the animal in some way so that you do not inadvertently sell or slaughter the animal before the drug withdrawal time is over. Remember that anything you inject into your animal becomes a drug. A few years ago, goat producers decided to dehorn their goat kids by injecting clove oil under the skin at the horn bud. FARAD does not have enough data on the use of injected clove oil as it is not a drug and research has not been done to see what effects it may have in animals. Therefore, due to lack of available data, it was determined that kids treated with clove oil injections should never enter the food chain.
Read the label. If the product you are using has a withdrawal time listed for sheep, make sure you give it exactly as directed, do not exceed the maximum dose allowed in one injection site and do not give it for a longer period than is listed on the label. Remember that the withdrawal time starts from the LAST dose that you administered not the day that you started treatment. If you are using a prescription drug, it should come with a label listing the withdrawal time for the species that it was prescribed for. If in doubt, always ask your veterinarian. Be careful using drugs prescribed for your cattle in sheep as some drugs like Baytril (enrofloxacin) is not allowed to be used in sheep at all. Your veterinarian can get drug withdrawal times for any drugs (prescription or OTC) from FARAD, and you should check with your veterinarian before using any drug extra label.
Editors Note: For interested in the Resources used for this article or becoming a member of the EAPK, be sure to check out their page!