Abstract

The anesthesia of blackbucks (Antilope cervicapra) in an exhibit at Tierpark Hagenbeck in Hamburg, Germany was compared to a group of free-ranging blackbucks at the Wildlife Safari in Winston, Oregon, USA. Both methods of immobilization (xylazine-ketamine in Hamburg and xylazine-tiletamine-zolazepam in Winston) achieved a smooth induction and a very good immobilization. The reversal was carried out with a combination of yohimbine and/or atipamezole in Hamburg and only atipamezole in Winston. In Hamburg the best results were obtained by a combination of yohimbine administered intramuscularly and atipamezole intravenously. In Winston only atipamezole was used and delivered a smooth recovery. Both methods enabled the animals to be released into the herd within a few hours.

Introduction

Institution A: Wildlife Safari Winston, Oregon, USA

Wildlife Safari keeps a group of free-ranging blackbucks in a drive-through area of 36.4 ha, together with yak (Bos grunniens), sika deer (Cervus nippon pseudoaxis), nilgai (Boselaphus tragocamelus), guanaco (Lama guanicoe), fallow deer (Dama dama) and ratites (Dromaius novaehollandiae, Rhea americana).

Institution B: Tierpark Hagenbeck, Hamburg, Germany

Tierpark Hagenbeck in Hamburg has kept blackbucks (Antilope cervicapra) for many years. Animals are frequently anesthetized for physical examinations, medical procedures, or transports to other institutions.

The anesthetic agent xylazine (2(2,6-dimethylphenylamino)-4-H-5,6-dihydro-1,3-thiazine hydrochloride) stimulates the α₂-receptors of the central nervous system and, therefore, inhibits the release of adrenaline and serotonine. In sufficient doses the sedative provides central muscle relaxation and analgesia.¹ Often xylazine is used in combination with ketamine hydrochloride (2-(o-chlorophenyl)-2-methylamino cyclohexanone hydrochloride). Ketamine belongs to the dissociative anesthetic agents and produces catalepsia and analgesia.¹ The combination of both drugs achieved good results in ruminants.^2,9 Another possibility is the combination of an α₂-agonist with tiletamine and zolazepam (Telazol (tiletamine hydrochloride and zolazepam hydrochloride)). Tiletamine is a dissociative agent that is comparable but more effective than ketamine. Zolazepam is a Pyrazolodiazepinone and has been used as a tranquillizer and anticonvulsant. The combination of tiletamine and zolazepam (TZ) has been widely used to immobilize wild animals.^3,6 To reduce the amount of TZ and decrease the risks of convulsion and excitation xylazine was added to the drug combination with good results.⁸ The sedative effect of xylazine can be reversed with α₂-adrenoceptor antagonists yohimbine hydrochloride or atipamezole (4-(2-ethyl-2,3-dihydro-1H-inden-2-yl)-1H-imidazole hydrochloride).⁴

In the past there have been reports on the use of xylazine in combination with the antidote yohimbine in this species. Strauss described the inefficiency of anesthetizing five blackbucks with 4.4 mg/kg xylazine and trying to reverse it by useing 2.0 mg/kg yohimbine.⁷ Unfortunately this was not a great success. On average the animals did not recover until approximately 251 minutes after yohimbine-injection.

Material and Methods

In Winston, blackbucks have been anesthetized with a combination of xylazine, tiletamine, and zolazepam. The body weight of the animal was estimated and the drugs were administered into the thigh muscles via dart (Pneudart®) delivered with a rifle (Dan-inject®). The dosage used was 1.5 mg Telazol/kg BW and 1.6 mg xylazine/kg BW. The induction time was measured from the time when the dart hit the animal until the blackbuck became recumbent. Prior to antagonizing the anesthetic agents, the animal was placed in a wooden crate. 1mg Atipamezole (Antipamezolhydrochloride, Antisedan®, Pfizer, 5 mg/ml) for every 10 mg of xylazine was injected intravenously and the catheter was removed. The time from reversal until the animal became sternal was recorded.

In Hamburg 52 blackbucks have been immobilized with a combination of xylazine and ketamine. Five hundred (500) mg xylazine (Rompun® Dry Substance, Bayer) was mixed with 5 ml ketamine hydrochloride (Ketavet®, Pharmacia and Upjohn, 100 mg/ml) to make a concentration of 100 mg xylazine and 100 mg ketamine per ml. The body weight of the animals were estimated and the drugs were administered into the thigh muscles via dart delivered with a blowpipe.

The induction time was measured from the time when the dart hit the animal until the blackbuck became recumbent. The animal was then positioned in right lateral recumbency. In thirteen animals a pulse oximetry probe was placed on the tongue or one of the ears and the pulse (beats/minutes) and the hemoglobin saturation (SpO₂) was recorded. After the procedure was completed the anesthetic agents were antagonized with different drugs and routes of administration.

Regarding the various antidotes and administration routes the animals in Hamburg can be divided into four groups:

• Group 1: 1.3 animals received an intravenous (IV) injection of only yohimbine (Yohimbin-HCl 1%).
• Group 2: 0.1 blackbuck was given atipamezole (Atipamezolehydrochloride, Antisedan®, Pfizer, 5 mg/ml) intramuscularly (IM).
• Group 3: 2.6 animals were reversed with a combination of yohimbine IV and atipamezole IM.
• Group 4: 16.23 animals were injected with a combination of yohimbine IM and atipamezole IV. The time between the injection and animal standing for the first time was recorded.

Results

A reference list of hematologic and biochemical data of animals aged 4–8 months and 2.0 adult blackbucks in Winston and Hamburg are given in Tables 1, 2, and 3.

Table 1. Institution A in Winston

^aT= Telazol
^bX= Xylazine

Table 2. Institution B in Hamburg

^aSa=sub-adult
^bAd=adult

^cT=Telazol
^dX=Xylazine
^eYo=Yohimbine
^fAt=Atipamezole

Table 3. Biochemical data

Discussion

Induction with both ketamine and xylazine (KX) and tiletamine, zolazepam, and xylazine (TZX) was rapid and smooth in both institutions. Immobilization with the combination of xylazine and ketamine and xylazine, tiletamine, and zolazepam has been reported as very efficient for ruminants in the literature for a long time. Wiesner recommended 0.1 ml of the “Hellabrunner mix” in subadults to 0.4 ml in adults for anesthesia in blackbucks. One milliliter of the “Hellabrunner mix” contains 12.5 mg xylazine and 10 mg of ketamine.¹⁰ The effects of xylazine can be reversed with the α₂-adrenoceptor antagonist yohimbine. The recommended dose for the antagonist is 0.125–0.25 mg/kg body weight intravenously or intramuscularly.⁵

Strauss immobilized five blackbucks and antagonized the anesthetic effects with an average of 1.65 mg yohimbine/kg body weight.⁷ No desired effect occurred and, therefore, he concluded that yohimbine is not the recommended antagonist for a xylazine anesthesia in blackbucks. In group 1 at Tierpark Hagenbeck an average dose of 0.75 mg yohimbine/kg BW was injected intravenously and mean recovery time was 24–25 minutes. This was not very satisfying because the time of recovery should be as short as possible after procedures are done to get the animal back to the group. Jalanka and Roeken reported on the successful use of atipamezole as a reversal for xylazine at a dose of 1 mg of atipamezole for every 8–12 mg of xylazine.⁴ In group 2, 0.21 mg atipamezole/kg BW was used to reverse the immobilization of a 1.5-month-old female. After 33 minutes the animal was able to stand for the first time. During the recovery the animal was struggling a lot. The animal was anesthetized previously and reversed with yohimbine and there was no struggling at that time. That lead to the conclusion that atipamezole alone was not a good reversal for a xylazine-induced anesthesia in these animals. This method was not further tested. In group 3 yohimbine and atipamezole were used at the same time. An average of 0.72 mg yohimbine/kg body weight was delivered intravenously and a mean dose of atipamezole at 0.12 mg/kg body weight intramuscularly. The mean recovery time for the entire group was 18.5 minutes. This was better than in the groups before but still too long and, therefore, the administration route had to be changed. In the last group at Hamburg the method that is used successfully at the Tierpark Hagenbeck today was established. Yohimbine was given IM in an average dose of 0.81 mg/kg BW and atipamezole at 0.12 mg/kg BW but this time intravenously. The amount of drug administered has not been changed significantly in the last two groups but the route of administration has made the difference. The average recovery time in 38 animals has been 3.92 minutes. In Winston atipamezole was given by itself and provided smooth and rapid recoveries.

Conclusion

The comparison of anesthesias in both institutions led to the conlcusion that both drug combinations are a valuable method to induce and maintain a safe immobilization in blackbucks. The recovery with either yohimbine + atipamezole or only atipamezole showed no significant differences, therefore the use of yohimbine in combination with atipamezole does apparently not increase the efficiency.

Literature Cited

1.  Fritsch R. Allgemeine pharmakologische und klinische Grundlagen der Immobilisation. DVG Tagung Tierpark Hellabrunn München. 1990:13–26.

2.  Gray CW, Bush M, Beck CC. Clinical experience using C1744 in chemical restraint of exotic specimens. J Zoo Anim Med. 1974;5:12–21.

3.  Hugues F, Leclerc-Cassan M, Marc JR. Anesthésie des animaux non domestiques, essai d´un nouvel anesthésique. L`Association Tiletamin/Zolazepam (Zoletil.N.I.). Rec Med Vet. 1986;162(3):427–431.

4.  Jalanka HH, Roeken BO. The use of medetomidine, medetomidine-ketamine combinations, and atipamezole in nondomestic mammals: A review. J Zoo Wildl Med. 1990;21:259–282.

5.  Jalanka HH. Medetomidine, medetomidine-ketamine combinations and atipamezole in nondomestic mammals: A clinical, physiological and comparative study. Academic dissertation, Department of Clinical Sciences, College of Veterinary Medicine. Helsinki, Finland. 1991.

6.  Schobert E. Telazol-Use in wild and exotic animals. Vet Med. 1987;82(10):1080–1088.

7.  Strauss G. Mangelhafte Effektivität von Yohimbin als Antidot des Xylazins bei der Immobilization von Antilopen. Verh.ber.Erkrg.Zootiere 1991;33:183–186.

8.  Thurmon JC, Lin HC, Benson GJ, Tranquilli AW, Olson WA. Combining telazol and xylazine for anaesthesia in calves. Vet Med. 1989;84(8):824–829.

9.  Wiesner H. Zur Neuroleptanalgesie bei Zootieren und Gatterwild unter Anwendung des Telinject Systems. Kleintierpraxis. 1975;20:18–24.

10.  Wiesner H. Praxis der Wildtierimmobilisation. DVG Tagung Tierpark Hellabrunn München: 1990:27–43.