Dart failures: Have they happened to you?

Darts generally remained in animals for about an hour in the Iowa State tests. Four of 15 darts failed to inject their medication in this trial.

The use of pneumatic darts for remote drug delivery (RDD) has become increasingly popular as a tool for treating sick cattle in the field, particularly in remote or inaccessible pastures where it is difficult or risky to capture, restrain or transport animals for conventional treatment. The practice has raised concerns, however, particularly in terms of beef quality assurance, due to potential for improper injection sites, inappropriate doses of antibiotics, injury to animals, broken needles remaining in cattle and a long list of other possible consequences.

Watch for our September 2016 issue for comprehensive coverage of the RDD issue. Meanwhile, we are interested to hear of your experiences with the mechanical function of RDD darts in the field.

In response to the rapid growth in the use of pneumatic darts for delivering antibiotics to cattle, researchers at several universities currently are conducting tests to evaluate the systems for drug delivery, disposition and efficacy, impacts on meat quality and other factors.

At Iowa State University, a team of researchers led by Hans Coetzee, BVSc, Cert CHP, PhD, DACVCP, DACAW, recently complete an experiment evaluating the use of RDD for treatment with tulathromycin, and resulting physiological effects on the animal.

Tulathromycin (Draxxin™) is a macrolide antibiotic indicated for the treatment of bacterial infections associated with bovine respiratory disease complex, infectious bovine keratoconjunctivitis and interdigital necrobacillosis. Low injection volume and long duration of activity after a single injection has resulted in tulathromycin becoming a popular choice for RDD in cattle, but the researchers note a lack of data describing the impact of RDD on injection site tolerance and tissue residue depletion.

In this test, the researchers used 15 Holstein calves weighing between 750 and 900 pounds, injecting each with 10 mL of tulathromycin using a pneumatic dart equipped with a ¾-inch, 14-gauge needle.

The researchers restrained each animal in a mobile chute and delivered the dart from a consistent distance of 9.1 meter, or just under 30 feet. Following the injections, they collected blood samples from each calf to measure levels of tulathromycin, cortisol, creatine kinase (CK) and aspartate aminotransferase (AST). They also used thermography, visual measurements and mechanical nociceptive threshold (MNT) assessment to measure inflammation and pain at injection sites and euthanized three animals at 24 hours post-treatment to inspect injection sites at necropsy.

In this trial, the researchers identified each dart with the individual tag number of the animal receiving it. The darts remained in the animals for an average of just over one hour. After collecting the darts, the researchers used visual inspection and dart weights to determine that four of the 15 darts did not properly inject the medication. Those four darts weighed an average of 24 grams compared with 13.5 grams for the darts that successfully injected the medication.

Coetzee says the darts use an explosive cap that normally forces a plunger forward to deliver medication upon impact with the animal. In the four darts that did not inject in this test, it appeared the cap did not detonate. Those four animals ended up serving as a control group for parts of the study, as they had experienced the impact of the dart but had not been injected with the drug.

Some inflammation and tissue reaction at an injection site is typical, which is why BQA guidelines call for injections in the neck, rather than in locations corresponding with high-value beef cuts. With a visual inspection 24 hours after treatment, the researchers immediately noticed that the four non-injected animals did not show significant swelling at the injection site, while the remaining 11 animals had various degrees of visible inflammation.

Thermography confirmed that assessment. In calves where RDD was successful, the mean minimum temperature at the dart site was 30.14ºC and mean maximum was 36.64 ºC compared to 26.10ºC and 36.03 ºC   in calves where RDD was unsuccessful.

The researchers used MNT, a pressure test to measure pain sensitivity, testing the right, non-injected, neck and the left injected neck at the injection site. In calves where RDD was successful, the difference in MNT tended to be greater at 6 and 24 hours after injection compared to calves where RDD was not successful.

The researchers also found higher concentrations of creatine kinase (CK), aspartate aminotransferase (AST) and cortisol in the calves that were successfully injected, indicating ongoing tissue reactions and stress compared with the four non-injected calves.

Three of the calves were euthanized for necropsy at 24 hours post treatment, and the researchers conducted macroscopic and microscopic examination of the injection sites. One of the calves showed evidence of mild subcutaneous hemorrhage with no gross muscle lesions. This calf was later identified as being in the dart failure group. Based on necropsy examination, the researchers determined that one of the darted animals received the drug deep into the muscle, while the other showed reactions consistent with the intended subcutaneous injection. “In my opinion it is this variability in delivery site that is the primary BQA concern,” Coetzee says.

The researchers also concluded that a significant incidence of failure of the RDD device to inject medication could present problems for producers. Coetzee notes that, unlike RDD of compounds intended to provide chemical restraint, pneumatic dart administration of antimicrobials produce no observable changes in animal behavior or demeanor that would indicate successful drug delivery. Given that darts may remain in the animal for up to an hour after delivery in a production setting, a producer might not be able to determine whether an animal was successfully treated or not.

What have you seen in the field, with either our own or your clients’ use of RDD? Please send your comments to me at [email protected].

Watch for the September issue of Bovine Veterinarian for more comprehensive coverage of RDD cautions and suggestions for minimizing risk in RDD use.