Abstract

Field immobilization of exotic hoofstock in large herds presents significant challenges for animal and human safety. Animals may experience heat stress and/or capture myopathy during immobilization. Aggression toward darted animals or team personnel from other animals and danger from environmental hazards (e.g., waterways) are further concerns. Precise anesthetic dosing that minimizes induction time is essential. Strategic coordination of personnel for efficient darting, capture, and removal of the animal from the field are paramount to success. Animals chemically immobilized in open environments amid numerous other hoofstock may respond differently than those in confined exhibits. Species variation in tendencies to sprint for significant distances following darting with various drug combinations, relative species sensitivity to α-2 agonists, and herd interactions affect immobilization outcomes. Anesthetic regimens were designed for reliable, rapid induction of exotic hoofstock in expansive field settings at a park exhibiting hundreds of African and Indian species. Opioid/xylazine combinations were used in impala (Aepyceros melampus), greater kudu (Tragelaphus strepsiceros), waterbuck (Kobus ellipsiprymnus), wildebeest (Connochaetes taurinus), and zebra (Equus burchelli). Telazol combined with ketamine and xylazine was used in blackbuck (Antilope cervicapra), mouflon (Ovis musimon), and nilgai (Boselaphus tragocamelus).

Introduction

The need for population management of several herds of nondomestic ungulates afforded a unique opportunity to refine anesthetic dosages and field strategies for immobilization. Lion Country Safari is a “drive-through” preserve exhibiting several bovid and equid species. Geographic features of the park, including numerous water bodies, provided a major impetus for refining immobilization protocols to minimize induction times. The large mixed herds also offer the potential for aggression toward darted animals. Many of these procedures are performed within public view underscoring the need for safe, efficient animal immobilization.

Materials and Methods

All animals reported here were darted in the field except for six of eight nilgai anesthetized (darted) in a barn. All animals were apparently healthy and weighed soon after immobilization. Prior to darting, a field team met to discuss approach strategies, vehicle positioning during induction, and animal support for veterinary procedures. Communication between field team members was done by two-way radio. Environmental temperatures were frequently between 28–35°C during immobilizations. Anesthetic dosages may be higher for animals darted in hot weather.²

Results and Discussion

Opioid/xylazine combinations (see Table 1 for drug dosages).

Table 1. Drug dosages

^aAll drug dosages average in mg/kg; route of administration = carfentanil IM, xylazine IM, naltrexone 1/4 IV, 3/4 SC, etorphine IM, Tolazine 1/2 IV, 1/2 IM (IM recommended for tolazine).
^bWaterbuck (Kobus ellipsiprymnus), wildebeest (Connochaetes taurinus), zebra (Equus burchellii).
n = number; DT = dart time (average minutes from darting until sternal); PT = procedure time (average minutes from sternal until reversal); RT = reversal time (average minutes from injection until standing).

Waterbuck

Approximately 130 waterbucks resided with 44 wildebeests, 31 elands (Taurotragus oryx), 8 mouflons, and 14 ostriches (Struthio camelus) in a large preserve bordered by canals and sloughs. They were generally easy to approach and had the potential to sprint long distances when administered opioids. Adult males exhibited aggression to darted waterbucks. The ostriches would occasionally block the darting vehicle, eat syringes, and peck the field team. These dosages were used to reduce sprinting after darting. Five young animals, 41–58 kg, included in data had higher mean dosages of carfentanil (ZooPharm, Fort Collins, CO, USA; 0.019 mg/kg) and xylazine (Phoenix Scientific, St. Joseph, MO, USA; 0.9 mg/kg) compared to the group. Younger animals may require higher anesthetic dosages than older animals.² An adult male (155 kg) was immobilized in field and barn settings >12 times for treatment of interdigital dermatitis. Supplemental oxygen was used to reduce hypoxemia. Respiratory depression was treated with doxapram (Dopram, Fort Dodge Animal Health, Fort Dodge, IA, USA; 0.4 mg/kg, IV) or 25% of the total tolazine (Congaree Veterinary Pharmacy, Cayce, SC, USA) dosage early in the procedure. Improved muscle relaxation was seldom needed but could be achieved with low dosage diazepam (Valium, Abbott Laboratories, North Chicago, IL, USA; 0.1 mg/kg, IV). The primary author believes that an adverse reaction to intravenous tolazine caused fatal or nearly fatal pulmonary edema in two waterbucks and one Nile lechwe (Kobus megaceros) not reported here. Intramuscular administration of tolazine is recommended.

Wildebeest

Wildebeests were fairly easy to approach although they sometimes required herding toward the darting vehicle. They did not sprint after darting. Aggression from other wildebeests and male waterbucks toward the darted animal was not observed. Induction was very smooth and quick.

Zebra

Approximately 56 zebras and 10 wildebeests resided together in a preserve immediately adjacent to canals and sloughs. The zebras were wary of field vehicles and the entire herd could panic if any animal was startled. The darting vehicle slowly approached the individual to be darted while the field team hid behind brush until the dart was fired. Field vehicles then emerged to block waterways. This long-established herd has strong social bonds and females sometimes guarded an individual selected for immobilization, blocking darting attempts. Aggressive posturing from mares toward the field team occurred when their young offspring were darted. Zebra would sprint and “high-step” after darting with opioids. The dosages used reduced induction time and high-stepping as compared to similar etorphine dosages combined with lower dosage xylazine. Muscle relaxation was generally good and was sometimes improved with a single bolus of detomidine (Dormosedan, Pfizer Animal Health, Exton, PA, USA; 5 mg IV) and/or butorphanol (Torbugesic, Fort Dodge Animal Health, Fort Dodge, IA, USA; 5 mg IV) Low dosage diazepam (0.05–0.1 mg/kg) was also used to improve relaxation. We have used similar dosages of etorphine and xylazine in more than 20 immobilizations of zebras weighing up to 309 kg, including an individual immobilized multiple times for laceration repair. Procedure times have ranged from 20–75 minutes. Recoveries using naltrexone (ZooPharm, Fort Collins, CO, USA) were very quick (1–2 minutes). Dosage and route of administration of naltrexone (1/4 IV, 3/4 SC) may warrant revision given previous investigations with this drug.^1,4 Xylazine is not reversed. Zebras appear to tolerate and benefit from higher xylazine dosages. The domestic horse is more tolerant of α-2 agonists than the bovid.⁶

Greater Kudu

Field dosage for an adult male kudu (204 kg) was carfentanil (0.027 mg/kg) + xylazine (0.9 mg/kg) reversed with naltrexone (2.8 mg/kg 1/4 IV, 3/4 SC) and tolazine (2.45 mg/kg IM). Significant sprinting occurred if dosages were lowered. Multiple immobilizations for lameness and joint fusion were performed with similar dosages.

Mouflon

Mouflons were often difficult to approach in field vehicles. They quickly caught on to changes in routine indicative of darting attempts. Staff often attempted to disguise the darting vehicle by using cars or vans not field vehicles. Wildebeests postured aggressively toward darted mouflon and were warded off with field vehicles or by waving a towel. Anesthesia data: three apparently healthy male mouflons, at least 8 years to geriatric, 49–57 kg, were anesthetized for treatment of lameness, horn repair with Telazol (Fort Dodge Animal Health, Fort Dodge, IA, USA; 8.4 mg/kg) + ketamine (Fort Dodge Animal Health, Fort Dodge, IA, USA; 4.2 mg/kg) + xylazine (1.0 mg/kg). The mixture was prepared by mixing 2.5 ml ketamine (100 mg/ml) with 500 mg of powdered Telazol. An appropriate volume (2.3–2.5 ml) of this mixture was then placed in the dart to which the xylazine dosage was added. Time elapsed from darting until sternal was 3–6 minutes. Working time was 40–75 minutes. A single bolus of diazepam (5 mg IV) was sometimes used to prolong anesthesia time. Reversal was with yohimbine (Yobine, Lloyd Laboratories, Shenandoah, IA, USA; 0.1 mg/kg IV). Time elapsed from injection of yohimbine until the animal stood was 2–60 minutes, the latter value was for mouflon that received diazepam late in the course of anesthesia. Propofol (PropoFlo, Abbott Laboratories, Chicago, IL, USA; 0.5 mg/kg IV) was also used to lengthen anesthesia and can be considered as an alternative to diazepam. This Telazol, ketamine, xylazine dosage has been reliable for four other mouflon immobilizations. Time elapsed from darting until sternal may be up to 14 minutes if mouflon have been excited and attempt to evade darting vehicle. Lower field dosages were not effective.

Nilgai

Approximately 45 nilgais, 180 blackbucks, 22 Asiatic water buffalos (Bubalus bubalis) reside in a preserve having thick vegetation, numerous canals, and sloughs. Nilgai are very skittish if they became aware of a darting attempt. They initially sprint hard after dart impact and tremendous herd excitement is exhibited. The darted individual and entire herd will effectively hide in brush after darting. Nilgai frequently cross waterways and will enter water after being darted. Aggression from other hoofstock has not been noted. Anesthesia data: eight adult male nilgais (205–209 kg) were anesthetized for castration (n=6) or vasectomy (n=2) with average dosages of Telazol (4.1 mg/kg) and xylazine (2.5 mg/kg.) Two were darted in the field, others were conditioned with food to come into a holding area, then darted in a barn to avoid risk posed by waterways. Time elapsed from darting until sternal was 2–6 minutes. Bouts of hyperpnea and presumed hypoxia sometimes occurred. Partial reversal of xylazine with 30–60% of a total tolazine dosage (2.5 mg/kg IM) was frequently given early in the procedure to improve ventilation. Anesthesia was sometimes lengthened with ketamine (2 mg/kg IM) or propofol (0.6 mg/kg IV). An additional six nilgai that were not weighed were successfully neutered with similar dosages. This regimen provided smooth anesthesia for neutering and did not result in the excessive thrashing and bouts of apnea that occurred with opioid/xylazine combinations.³ Nilgai often did not stand until 40–60 minutes after reversal. Refinement of this anesthetic regimen may be possible given recent work with other alpha-2 agonists.^5,7 Reduction of the xylazine dosage would be prudent in captive situations where maximum reduction of induction time is not critical. Nilgai may have rough recoveries when tolazine is given to reverse xylazine if ketamine has been administered within the previous 30–45 minutes.

Blackbuck

Nearly 80 blackbucks (27–39 kg) were darted with a standard 1.2 ml dose of a Telazol (500 mg) + ketamine (400 mg) + xylazine (100 mg) mixture for castration, vasectomy, or pre-shipment testing. Reliable induction times of 4–6 minutes from darting until sternal occurred. No reversal was given due to thrashing that occurred if tolazine was given. Animals did not stand for 3 hours post-dart. This regimen may be revised to preserve advantageous induction times and improve recovery times.

Supplemental oxygen is recommended for chemically immobilized hoofstock.

Acknowledgments

Thanks to Brian Dowling, Jen Robertson, Marsha Abrams, Ron Cameron, Terry Wolf, Sherri Garz, the animal capture team, and hospital staff of Lion Country Safari.

Literature Cited

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