Delivering drugs by darts can extend withdrawal times

Remote drug delivery systems such as dart guns are often used to administer sedation or tranquilizers to wildlife species that need to be restrained. Dart guns can also be used to administer tranquilizers to cattle that have escaped and can’t be restrained in holding facilities.

It appears that some of the newer pneumatic dart gun systems that fire lightweight darts are now being used in some specific situations to administer antimicrobial medications to cattle on pasture that require treatment for diseases such as foot rot or pneumonia.

The advantages of this type of delivery of therapy are obvious. In some of our western Canadian pasture systems, it may be a long distance to restraint and handling facilities. Restraint with lariats requires special skills and well-trained horses and any type of capture is going to introduce stress to the animal being treated. A remote drug delivery system, such as a pneumatic dart gun, solves many of these issues.

However, the use of these remote drug delivery systems creates other potential problems.

Dr. Roy Lewis wrote an excellent article in this column in The Western Producer several years ago on this subject. I would encourage readers to re-read that article online, which describes many of the pros and cons that must be taken into account and how to reduce potential problems when using a dart gun to administer antimicrobial medications.

One of the problems Lewis discussed was the limitation in the volume of medication that can be administered via a dart gun. This limitation often results in producers wanting to use an antimicrobial that has a small volume of administration, especially when treating adult cattle on pasture.

Tulathromycin is one of the antimicrobials licensed for cattle that requires a relatively small volume to be used to treat an animal and as a result, it is one of the products often used in remote drug delivery systems.

It should be noted that this is an “off-label” use of this product. The label for this particular antimicrobial drug is all determined with a subcutaneous injection. There is no label claim for administering this product via a pneumatic dart gun.

Tulathromycin has always been a product that requires a veterinary prescription. The recent changes to the laws around the prescription of all veterinary antimicrobials now requires that veterinarians have a veterinary-client relationship before prescribing any antimicrobials for on-farm use.

Two recent articles have been published in the Journal of Animal Science that have examined what happens when tulathromycin is administered with a pneumatic dart. Both articles were published by Dr. Hans Coetzee’s laboratory. Coetzee is a highly regarded veterinary clinical pharmacologist. He has recently moved to Kansas State University from Iowa State, where some of this research was originally done.

In the first of the two articles, Coetzee compared the local effects of administering tulathromycin via a dart gun system compared to the conventional injection method. He also compared the drug levels in the calves post-injection.

One of his key findings in this study was that four of the 15 calves that received the tulathromycin with the dart guns did not receive the entire dosage. In these calves, some of the drug was left in the dart and was not fully injected.

Obviously, this is an important issue; if cattle don’t receive the appropriate dose of drug, it may lead to more treatment failures.

This study also demonstrated that the calves that were darted had higher levels of stress hormones after injection, had more evidence of muscle damage and more pain at the injection site than the calves that received tulathromycin with the conventional sub-cutaneous injection.

The second of the two articles used male Holstein calves, and tulathromycin was administered to all of the calves via a pneumatic dart system. Calves were then euthanized at various times post-injection to determine the tulathromycin concentrations in various tissues and to examine the tissue damage caused by the darts.

The results of the study suggested that using darts created significant injection site reactions in these calves and that the withdrawal times indicated on the label would not be accurate when administering this product via a pneumatic dart. Withdrawal times would need to be extended beyond what was indicated on the label.

This was a very small study involving only 14 calves and therefore the conclusions were limited, but it did show that the indicated label withdrawal times should probably be extended if tulathromycin was administered with a remote drug delivery system.

The Beef Quality Assurance Guidelines in the United States issued an advisory statement regarding the use of pneumatic darts in cattle and it is available on its website. It lists many issues of concern when using pneumatic dart guns, such as concerns about the route of administration (subcutaneous versus intramuscular), tissue damage, “off-label” withdrawal times and the possibility of broken needles being lodged in tissues.

Remote drug delivery systems are an important issue that requires more research and some stronger guidelines on appropriate use.

Food safety, antimicrobial stewardship and quality assurance have always been top priorities for the beef industry and we have made some good progress in reducing injection site lesions and getting the message out about proper injection techniques.

Remote drug delivery systems such as pneumatic dart guns may be one of the only options available to some producers to provide treatments to cattle in remote locations and because of this it is an important animal welfare issue.

However, we need more research to establish appropriate withdrawal times and to examine how these products can be given in a safe and prudent fashion.

John Campbell is a professor in the department of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.

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