Immobilization of Captive Wapiti Cervus canadensis with Azaperone and Xylazine

North American wapiti Cervus canadensis, also known as elk, is one of the largest species within the Cervidae family. Captive and free-ranging populations of wapiti are highly prevalent, warranting the need for a quick and safe immobilization protocol for implementing routine herd health, diagnostic, and disease monitoring programs (Corn and Nettles 2001; Hattel et al. 2007). One of the earliest reports for immobilizing wapiti described the use of carfentanil, an ultrapotent morphine-like agent belonging to the fentanyl family of narcotics (Meuleman et al. 1984). Although an effective immobilization agent, carfentanil limitations include a 5–10% incidence of renarcotization in ungulates after reversal (Allen 1989) and life-threatening hazards to humans if handled inappropriately (George et al. 2010). Different combinations of drugs have also been reported to be effective in wapiti that include another potent opioid, etorphine hydrochloride/M99 (Magonigle et al. 1977), ketamine–xylazine (Golightly and Hofstra 1989), and xylazine–tiletamine–zolazepam (Read et al. 2001). Both tiletamine and ketamine are dissociative anesthetics that run the risk of causing convulsive activity and rigidity if not administered with tranquilizers or if reversal occurs too quickly (Caulkett 1997). For routine preventative procedures (blood testing, deworming, vaccinations, deantlering), the use of a dissociative anesthetic to induce a deep plane of anesthesia is usually not necessary and introduces the risk of causing aspiration pneumonia, respiratory arrest, and/or death (Carroll and Hartsfield 1996).

In free-ranging Rocky Mountain elk Cervus canadensis nelsoni, a combination of butorphanol, azaperone, and medetomidine has been described as a safe and effective immobilization agent (Wolfe et al. 2014a). Butorphanol is a partial opiate agonist that contains both analgesic and sedative properties and can be reversed with naltrexone (Wolfe et al. 2014a). Azaperone is a short-acting neuroleptic sedative that can reduce stress from capturing and handling in combination with other drugs (Caulkett and Arnemo 2014). The final component, medetomidine, is a potent α2-adrenoreceptor agonist that has effective sedative and analgesic properties and allows for good muscle relaxation, but it can also be easily reversed (Wolfe et al. 2014a). Although one article reported that medetomidine and azaperone in combination were insufficient for handling free-ranging Rocky Mountain elk (Wolfe et al. 2014b), another article reported that a combination of 1 mg/kg body weight (BW) of a different α2-adrenoreceptor agonist, xylazine, and 0.1 mg/kg BW azaperone is effective for sedation in wapiti (Caulkett 1997). However, there is a lack of published data to support the use of this combination of xylazine and azaperone alone for immobilization in captive wapiti. Therefore, the goal of this project was to determine the efficacy and safety of a combination of xylazine and azaperone for immobilizing captive North American wapiti by 1) recording induction and reversal times and 2) measuring temporal physiological responses of arterial blood gas and electrolyte parameters to immobilization.

To avoid unnecessary immobilization, data were collected opportunistically during routine processing of Rocky Mountain wapiti performed at two separate facilities in Illinois. Techniques were consistent with guidelines approved by the American Society of Mammalogists (Sikes 2016). The first round of immobilization occurred November 2016 at the Busse Woods Forest Preserve in Elk Grove, Illinois, USA. The small wapiti herd (n = 6) at this facility inhabit a 17-acre (6.8-ha) enclosed pasture and had previously tested negative for both Brucella abortus and Mycobacterium bovis. Wapiti were moved to a 50 × 30 m holding pen and remotely immobilized in succession. The second round of immobilization occurred February 2017 at a privately owned facility in east central Illinois. These captive wapiti (n = 6) are rotated throughout an 8-acre enclosed pasture and previously tested negative for Brucella abortus and Mycobacterium bovis. The second set of wapiti were moved to a 40 × 40 m holding pen and remotely immobilized in succession. Three female wapiti from the second herd were immobilized August 2017 for pregnancy diagnosis via rectal palpation, during which physiological parameters were monitored. All wapiti were approached and darted from no farther than 10-m distance.

We immobilized wapiti (n = 7 adult females, n = 4 adult males, n = 1 male calf) at both facilities within the natural breeding season (September–February). Xylazine hydrochloride was dosed at 400 mg for bulls (1 mL, 300 mg/mL; Zoopharm, Windsor, CO; 1 mL, 100 mg/mL; AnaSed LA, VetOne^®, Boise, ID), 300 mg for cows (1 mL, 300 mg/mL; Zoopharm), and 125 mg for an approximately 6-mo-old calf (1.25 mL, 100 mg/mL; AnaSed LA, VetOne). Azaperone tartrate (50 mg/mL; Zoopharm) was dosed at 50 mg for all adult animals and at 15 mg for the calf. Using estimated animals' weights based on clinical experience, dosages were calculated to be approximately 1.3 mg of xylazine per kilogram of BW (1.3 mg/kg BW) and 0.2 mg/kg BW azaperone (Table 1). All injections were delivered remotely to the quadriceps musculature by an experienced clinician using powder-charge darts (3.0 mL for bulls and 2.0 mL for cows and calf) with gel collars with 1.25-in. (3.2-cm) needles (Pneu-Dart Inc., Williamsport, PA) fired from a CO₂-powered rifle (X-Caliber^TM; Pneu-Dart Inc.). We monitored initiation of immobilization (minutes), defined as the time from remote injection until the head began to drop, and induction time (minutes), defined as the time from remote injection until the animal was completely down and able to be approached. When wapiti were approached, towels were placed over their eyes to minimize visual stimulus.

During immobilization, we recorded heart rate via thoracic auscultation (beats per minute), respiratory rate by visual examination of thoracic movement (breaths per minute), and rectal temperature with a digital thermometer (Celsius). We performed routine processing of all wapiti during the period of immobilization. Processing included administration of vaccines against common bacterial (Covexin 8; Merck, Kenilworth, NJ) and respiratory (Vira Shield^® 6; Elanco, Greenfield, IN) pathogens subcutaneously and a topical dewormer (Cydectin; Bayer Corporation, Whippany, NJ). In November, antlers also were removed from bulls by using an electric saw. We performed venipuncture in all animals in the February collection and one animal in the November collection for routine herd screening.

After completing the procedures, we administered tolazoline hydrochloride (100 mg/mL, Tolazine^® HCl; Akorn, Inc., Lake Forest, IL) intramuscularly at 1,200 mg for larger bulls, 900 mg for smaller bulls and cows, and 300 mg for the calf. We administered an extra 400 mg of tolazoline to one bull (total 1,600 mg) after he did not respond to the initial dose. Using estimated animal weights, we administered the approximate dose of tolazoline 3 mg/kg BW (Table 2). We recorded recovery time (minutes) from the time of reversal administration until the animal was standing.

After determining the efficacy of using this xylazine and azaperone protocol, we used the same protocol (300 mg of xylazine plus 50 mg of azaperone) to immobilize a subset of three mature female wapiti (ages 3–10 y) for routine pregnancy diagnosis via rectal palpation. To better evaluate physiological responses to the drugs, we obtained an anaerobic 1-mL blood sample from the medial auricular artery at 0, 30, and 60 min after the wapiti were completely immobilized. We measured blood gases by using a portable analyzer (VetScan i-STAT 1; Abbott Point of Care Inc., Union City, CA), and determined lactate by using a handheld lactometer (Lactate Plus meter; Nova Biomedical, Waltham, MA). We performed drug reversal as previously described with 900 mg of tolazoline, and recovery was uneventful.

All data are presented as mean ± standard deviation (SD). In total, we successfully immobilized 11 (92%) of 12 wapiti with an estimated dose of 1.3 ± 0.05 mg/kg xylazine and 0.2 ± 0.03 mg/kg azaperone administered intramuscularly (Table 1). For these 11 wapiti, we noted initial signs of immobilization (head drop) at a mean of 5 min 49 s (range: 2–9 min), and achieved complete immobilization at a mean of 6 min 40 s (range: 2–12 min; Table 2). The remaining adult female required a second dart that contained 200 mg of xylazine and was successfully immobilized within 5 min (Table 2). Heart rate, respiratory rate, and rectal temperature (Table 1) were within recommended limits for this species (Caulkett and Arnemo 2014). We administered tolazoline intramuscularly at an estimated dose of 3.0 ± 0.6 mg/kg with wapiti standing at a mean of 8 min 50 s (range: 3–14 min) after reversal administration (Table 2).

In the three wapiti used for measuring arterial blood gas and electrolytes, we immediately observed a moderate hypoxemia via hypoventilation and ventilation-perfusion mismatch as depressed partial pressure of arterial oxygen and increased partial pressure of arterial carbon dioxide (Table 3). However, the depressed partial pressure of arterial oxygen resolved by 60 min, before reversal. The remaining physiological parameters of these immobilized wapiti cows remained relatively stable throughout the collection period (Table 3).

We found that a combination of xylazine and azaperone was safe and effective for immobilization of captive North American wapiti. The estimated doses reported in the current study were chosen based on clinical experiences of one author (CFS) and are slightly higher than those suggested previously for captive wapiti (Caulkett 1997) at 1.3 mg/kg xylazine and 0.2 mg/kg azaperone vs. 1 and 0.1 mg/kg, respectively. A major advantage of using this combination of drugs in both captive and wild wapiti, where weight is generally estimated, is their wide safety margin (Walter et al. 2005; Wolfe et al. 2014a). Doses of 0.11, 0.17, and 0.22 mg/kg azaperone were previously used in combination with low, medium, and high doses of butorphanol and medetomidine, with transient hypoxemia reported in all wapiti that resolved after medetomidine reversal (Wolfe et al. 2014a). Another study reported no apparent side effects with up to 3 mg/kg xylazine administered remotely in conjunction with tiletamine and zolazepam (Telazol^®; Fort Dodge Laboratories, Inc., Fort Dodge, IA) to free-ranging wapiti (Walter et al. 2005). The doses required to immobilize wapiti seem to be affected by individual animal physiology and behavior, which may be why another author reported insufficient immobilization with medetomidine and azaperone in free-ranging wapiti (Wolfe et al. 2014b). By contrast, no differences in induction time were detected between darted captive and free-ranging wapiti in another study with sufentanil (a potent opioid) and xylazine (Kreeger et al. 2011). Although all of the animals in the current study were considered to be captive rather than free ranging, the wapiti were not handled on a regular basis and were increasingly excited by the initiation of darting within each group. Regardless, further work is necessary to determine whether the estimated doses of xylazine and azaperone evaluated in this study would be sufficient for immobilization of free-ranging wapiti populations.

Quick immobilization induction times help to minimize stress and reduce the risks of injury, hyperthermia, and capture myopathy (Paterson 2007). The mean induction time of 6 min 40 s reported in the current study is faster than those reported in captive and free-ranging wapiti with xylazine–tiletamine–zolazepam (∼10 min; Read et al. 2001) and free-ranging wapiti with acepromazine–medetomidine (7–15 min; Wolfe et al. 2014b), but comparable to those reported for captive wapiti with butorphanol–azaperone–medetomidine (5–7 min; Wolfe et al. 2014a). Induction time in captive and free-ranging wapiti treated with 0.1 mg/kg sufentanil and 0.5 mg/kg xylazine was reportedly lower at 4.4 and 5.1 min, respectively (Kreeger et al. 2011). Although opioids are equally to more effective at reducing induction times than azaperone, they are controlled substances that require strict regulations in regard to storage, record keeping, and handling protocols. In addition, reported side effects with opioids include hyperthermia, poor muscle relaxation, and prolonged recoveries if not reversed (Caulkett et al. 2000). These results suggest that the addition of azaperone seems to be a safe alternative to opioids to reduce the induction time in captive wapiti.

Another advantage of the xylazine–azaperone immobilization protocol over others is the ability to antagonize the xylazine with tolazoline, while allowing the azaperone to persist with its sedative effects to reduce stress upon recovery in captive animals. Reported dosages for tolazoline administration in wapiti have ranged from 2 mg/kg (Kreeger et al. 2011) to 4 mg/kg (Walter et al. 2005). The estimated dose of 3 mg/kg tolazoline used in the current study appeared to be sufficient, with wapiti standing at a mean of 8 min 50 s after reversal at a range of 3–14 min. This recovery time is similar to reports of 7–12 min with butorphanol–azaperone–medetomidine (Wolfe et al. 2014a) but prolonged in comparison to the 3.9 min reported with sufentanil and xylazine (Kreeger et al. 2011). The prolonged recovery time is likely due to the persistence of azaperone, since both sufentanil and xylazine were previously reversed (Kreeger et al. 2011). The sedative effects of azaperone allow for a less stressful recovery from anesthetics and may outweigh the benefits of a faster, but more stressful, recovery in captive populations. Further studies in free-ranging populations may be necessary to determine whether the prolonged recovery time and subsequent sedation affects the ability of wapiti to escape predators or whether continuous monitoring would be required.

Normal arterial oxygen tension in ruminants is greater than 80 mmHg, and supplementation with oxygen is recommended while under anesthesia due to the risk of hypoxia (Carroll and Hartsfield 1996; Fahlman et al. 2014). Although we detected a transient hypoxemia immediately after immobilization in the current report, it was resolved by 60 min postimmobilization and did not seem to affect recovery. In addition, the observed hypoxemia in the current report was less pronounced than that described in wapiti immobilized with xylazine–tiletamine–zolazepam at 70 vs. 11.8 mmHg, respectively (Read et al. 2001). In this previous report, hypoxemia was successfully managed by simply supplementing with 5 min of nasal insufflation of oxygen at 10 L/min (Read et al. 2001). However, although improved arterial blood gas values may occur, supplemental oxygen increases the risk of causing prolonged periods of apnea and moderate-to-severe hypercarbia and respiratory acidosis in immobilized wapiti (Paterson et al. 2009). Therefore, since the hypoxia observed was transient and resulted in a normal recovery, oxygen supplementation seems unnecessary for use with the current protocol for short, routine procedures in wapiti.

We thank the staff at the Busse Woods Forest Preserve in Elk Grove, Illinois, for allowing us to use and publish data collected during routine wapiti processing. We also acknowledge University of Illinois clinical year veterinary students Samantha Scholz and Andrew Lee for assisting with data collection. Funding for this project was provided internally. The authors would also like to extend their utmost gratitude to the Associate Editor and reviewers for their invaluable input that greatly improved the final version of this manuscript.

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