Comparison of three anaesthetic protocols in Bennett s wallabies (Macropus rufogriseus)

Veterinary Anaesthesia and Analgesia, 2010, 37, 207 214 doi:10.1111/j.1467-2995.2009.00523.x RESEARCH PAPER Comparison of three anaesthetic protocols in Bennett s wallabies (Macropus rufogriseus) Tim Bouts*, Nicola Harrison, Karla Berry*, Polly Taylorà, Andrew Routh & Frank Gasthuys *Zoological Society London, ZSL Whipsnade Zoo, Veterinary Department, Whipsnade, Bedfordshire, UK Zoological Society London, Institute of Zoology, London, UK àtaylor Monroe, Gravel Head Farm, Ely, Cambridgeshire, UK Zoological Society London, ZSL London Zoo, Veterinary Department, Regents Park, London, UK Ghent University, Faculty of Veterinary Medicine, Department of Surgery and Anaesthesiology, Merelbeke, Belgium Correspondence: Tim Bouts, Zoological Society London, ZSL Whipsnade Zoo, Veterinary Department, Whipsnade, Bedfordshire LU6 2LF, UK. E-mail: tim.bouts@zsl.org Abstract Objective Investigate physiological and sedative/ anaesthetic effects of xylazine, medetomidine or dexmedetomidine combined with ketamine in freeranging Bennett s wallabies. Study design Prospective clinical trial. Animals Twenty-six adult free-ranging Bennett s wallabies. Methods Animals were darted intramuscularly with one of three treatments: xylazine and ketamine, 2.0 and 15.0 mg kg )1, respectively (XK): medetomidine and ketamine 0.1 and 5.0 mg kg )1 (MK) and dexmedetomidine and ketamine 0.05 and 5.0 mg kg )1 (DMK). Body weights were estimated. If the animal was still laterally recumbent after 45 minutes of anaesthesia, then an alpha-2 adrenoceptor antagonist, atipamezole, was administered (XK: 0.4 mg kg )1, MK: 5 mg kg )1, DMK: 2.5 mg kg )1 ). Heart rate (HR) and respiratory rate (f R ) were recorded at 5-minute intervals and temperature at 10-minute intervals. Venous blood was taken 30 minutes after initial injection. Statistical analysis utilized ANOVA. p < 0.05 was considered significant. Results Animals became recumbent rapidly in all groups. XK animals had muscle twitches, responded to external stimuli, and three animals required additional dosing; this was not observed in the MK and DMK groups. HR (mean ± SD beats minute )1 ) in XK (81 ± 4) was significantly higher than MK (74 ± 2) and DMK (67 ± 4). There were no differences in f R, temperature, blood-gas and biochemical values between groups. More animals in MK (9/10) and DMK (5/6) needed antagonism of anaesthesia compared with XK (1/10). There were no adverse effects after anaesthesia. Conclusion and clinical relevance Cardio-respiratory effects were similar in all groups. There were fewer muscle twitches and reactions to external stimuli in MK and DMK. Duration of anaesthesia was shorter in XK; most animals in MK and DMK needed atipamezole to assist recovery. All three treatments provided satisfactory sedation/anaesthesia and are suitable for use in Bennett s wallabies. Keywords alpha-2 agonists, Bennett s wallaby, dexmedetomidine, ketamine, medetomidine, xylazine. Introduction Marsupials are a large and diverse group of mammals spread over Australasia and the Americas. Wallabies, including Bennett s wallabies (Macropus rufogriseus), are a popular species in zoos and wildlife parks. Historically, the Zoological Society 207

London, Whipsnade Zoo (WZ) has kept wallabies since the 1930s (Bourne 1997). A population of about 600 Bennett s wallabies is presently free roaming on 700 acres of grassland at WZ. Consignments of wallabies are transferred to other European zoos to sustain local breeding programmes. As most wallabies and kangaroos (macropods) are kept in extensive enclosures or free roaming, routine treatment and examination are not possible without the use of chemical restraint (Unwin 2004). Furthermore, macropods are extremely sensitive to capture myopathy, making chemical restraint without physical exertion the preferred method for capture (Cole et al. 1994; Unwin 2004). Although there is no ideal sedative product for macropods, chemical restraint in this species has made considerable progress over the last few decades. The combination of zolazepam and tiletamine was successfully used by intramuscular (IM) injection in the red kangaroo (Macropus rufus) (Boever et al. 1977). This combination has been used for many years in different macropod species, either alone or in combination with isoflurane, ketamine and neuroleptic drugs (Shima et al. 1993). However, zolazepam tiletamine causes undesirable side effects. Although the excessive salivation can be controlled with atropine, the recovery is unduly prolonged (Holz 2005). Subsequently, medetomidine has been included in the combination, and, with a lower dose of zolazepam tiletamine and medetomidine antagonism with atipamezole, recovery time has been reduced (Unwin 2004). A range of doses of xylazine ketamine combinations has been used for some years in several species of wallaby, including the Bennett s wallabies at WZ (Richardson & Cullen 1984; England & Kock 1988). Respiration and blood-gas values were not significantly affected by the different doses, although bradycardia was observed in all protocols. However, induction was faster and the duration of anaesthesia longer in animals receiving the higher doses of xylazine (England & Kock 1988). More recently use of medetomidine ketamine was reported in Eastern grey kangaroos (Macropus giganteus) (Pye & Booth 1998). The cited doses produced light anaesthesia in most cases but occasionally heavy sedation in some animals. Most animals required administration of atipamezole to hasten recovery from sedation. Recovery was smooth when the antagonist was administered more than 24 minutes after initial injection. In contrast, animals receiving the antagonist prior to this time showed clear signs of anxiety and ataxia, most likely due to residual effects of ketamine. Doses of medetomidine (0.1 mg kg )1 ) and ketamine (5 mg kg )1 ) have been described as causing effects ranging from deep sedation to complete immobilization in five Bennett s wallabies. However, no specific details were reported (Jalanka & Roeken 1990). To the authors knowledge, there are no published reports describing the effects of dexmedetomidine in combination with ketamine in macropods. As the dose rate of dexmedetomidine in cats and dogs has been reported as half the dose of medetomidine (Ansah et al. 1998), a similar reduction in dose of dexmedetomidine is likely to be appropriate for macropods. Xylazine ketamine has been used historically for capture at WZ. The aim of this study was to investigate the physiological and sedative/anaesthetic effects of xylazine, medetomidine or dexmedetomidine combined with ketamine to determine the best protocol for anaesthesia in free-ranging Bennett s wallabies at WZ. Materials and methods Twenty-six (5 male and 21 female) free-ranging adult Bennett s wallabies (M. rufogriseus) were anaesthetized during June 2008, for translocation to a new exhibit at the Zoological Society London, London Zoo. The Ethics Committee at the ZSL was notified but because the procedure was part of the routine clinical work, ethical approval was not required. Wallabies were anaesthetized early in the morning to reduce possible heat stress and the likelihood of public interference. Anaesthesia was induced by remote injection of both drugs in one syringe in the hindquarters using a compressed air projectile syringe and a CO 2 powered rifle (Dan-Inject; IM Rifle, Somerset, UK). A range finder (Bushnell; Yardage Pro Sport, Surrey, UK) was used to estimate adequate darting distances and to apply correct dart pressures in order to minimize impact trauma. The animals were initially divided into three groups of 10 animals. The first 10 received XK, the second 10 MK, and, as ultimately only 26 wallabies needed translocation, there were only six animals in the DMK group. Doses were based on estimated body weights (BW) of 10 12 kg. XK (n = 10) received the 208 Ó 2010 The Authors. Journal compilation Ó 2010 Association of Veterinary Anaesthetists, 37, 207 214

Table 1 Scoring system used for assessment of sedation/ anaesthesia in Bennett s wallabies Score routine protocol used at WZ: 2.0 mg kg )1 xylazine (Rompun 2%; Bayer Plc, Berkshire, UK) and 15.0 mg kg )1 ketamine (Ketaset; Fort Dodge Animal Health, Southampton, UK) IM. MK (n = 10) received 0.1 mg kg )1 medetomidine (Domitor; Pfizer Limited, Kent, UK) and 5.0 mg kg )1 ketamine IM, (Jalanka & Roeken 1990; Holz 2003) and DMK (n = 6) received 0.05 mg kg )1 dexmedetomidine (Dexdomitor; Pfizer Limited, Kent, UK) and 5.0 mg kg )1 ketamine IM. The anaesthetist was aware of the drug combination injected in order to maximize safety for both the animals and staff. Immediately after darting, as most animals were aroused on impact of the dart before returning to indifference and a state of rest, the anaesthetist retreated to a safe distance to observe the animal closely and reduce the chance of it going into hiding. Once the animal was recumbent and nonresponsive to auditory stimuli, it was approached from behind. A blindfold was applied and initial measurements taken. Each anaesthetized animal was weighed in a Hessian bag on a dial hanging scale with hook (HIW50, CMS Weighing Equipment Ltd., London, UK). Heart rate (HR) and respiratory rate (f R ) were measured by auscultation and observation of the thorax, and recorded every 5 minutes throughout the procedure. Rectal temperature was measured every 10 minutes using a digital thermometer (DT- 11(A); Cox, Durham, UK). Venous blood samples were taken from the lateral tail vein for routine blood-gas analysis 30 minutes after darting, and blood-gas, electrolytes and biochemical parameters were measured using a hand held device (I-STAT hand held blood analyzer; Abbott, Berkshire, UK) with a test cartridge, (Chem 8 + ; Abbott, Berkshire, UK). During anaesthesia, all wallabies were transferred to an indoor holding enclosure to await transport. They were microchipped subcutaneously (SC) between the shoulder blades and were treated with ivermectin SC (Panomec; Merial Animal Health, Essex, UK), vitamin E and Selenium (Vitenium; Novartis Animal Health UK Ltd., Hertfordshire, UK) IM. If animals were not responsive to external stimuli and/or were still in lateral recumbency 45 minutes after the darting, then atipamezole (Antisedan; Pfizer Limited, Kent, UK) was administered (0.4 mg kg )1 in XK, (1/5 of xylazine dose); 0.5 mg kg )1 in MK, (five times medetomidine dose) and 0.25 mg kg )1 in DMK, (five times dexmedetomidine dose); half the dose was administered IM in the gluteal muscles and half IV into the lateral tail vein. Time in minutes from darting to first sign of sedation, recumbency, approach, sternal and standing were recorded. The degree of restraint (or sedation) was judged on clinical effect (presence or absence of muscle twitches and reaction to external stimuli) and scored using a simple descriptive scale ranging from 0 to 3 (Table 1). Statistical analysis Hierarchical repeated measures ANOVA was used to compare the repeated measurements in each anaesthesia group for HR, f R, and temperature for 35 minutes from the time of approach. Bonferroni s correction (post hoc test) was applied to determine where significance lay. One-way ANOVA was used to compare blood-gas data and the different times after induction from the three treatments. Levene s test was used to check for homogeneity followed by Bonferroni s post hoc tests. Where data were not normally distributed a Mann Whitney U test was used. Values of p 0.05 were considered statistically significant. All data are summarized and presented as mean ± SD. Statistical analysis was carried out on SPSS for Windows (SPSS Inc., IL, USA) Results Description 0 No effect; unable to approach the animal 1 Slight effect; unable to approach the animal 2 Light sedation; animal can be approached but is responsive to external stimuli. 3 Heavy sedation/anaesthesia; no response on external stimuli during procedure. The actual induction doses of ketamine and alpha-2 agonists administered in each group as well as the body weights are shown in Table 2. Three animals in the MK group could not be approached (2 animals: stage 0; 1 animal: stage 1) after initial darting, so a second dart was used. The top-up doses were estimated from the level of sedation achieved after Ó 2010 The Authors. Journal compilation Ó 2010 Association of Veterinary Anaesthetists, 37, 207 214 209

Table 2 Body weight of 26 Bennett s Wallabies and actual drug doses administered by dart to induce sedation/ anaesthesia Table 3 Times in minutes (mean ± SD) after darting for 26 Bennett s Wallabies to reach various states (without antagonism) following darting with one of three drug combinations (Table 2) Anaesthetic group Body weight Mean ± SD (kg) Anaesthetic drugs Drug doses Mean ± SD (mg kg )1 ) XK (n = 10) MK (n = 10) DMK (n =6) XK (n = 10) 13.3 ± 1.2 Xylazine 1.6 ± 0.02 Ketamine 11.9 ± 0.7 MK (n = 10) 12.7 ± 0.3 Medetomidine 0.1 ± 0.00 Ketamine 4.8 ± 0.04 DMK (n = 6) 11.3 ± 0.2 Dexmedetomidine 0.05 ± 0.00 Ketamine 5.3 ± 0.03 Three wallabies in the MK group required a second dart for technical reasons (see text). Three wallabies in the XK group received IV top-ups of 5 7.5 mg kg )1 ketamine when first restrained. Group XK received xylazine and ketamine, group MK, medetomidine and ketamine and group DMK dexmedetomidine and ketamine. first injection (score 0 animals: full dose; score 1 animal: half dose). In two of these animals the original dart had failed to discharge. As they had received no drug from the initial dart, all results and statistical analyses were based on the time the second dart was fired. The third animal had been injected in the pouch, most likely leading to loss of part of the dose, so times for this animal were calculated as from the first dart. Four animals became excited and were temporarily lost in the vegetation after darting (two animals in the XK group; BW: 11.8 and 15 kg and two animals in the DMK group; BW: 11.2 and 12 kg) but were found before initial effects were seen. While grasping the tail at first approach, three animals in the XK group (BW: 11.8 21.5 kg) had a flight reaction (score 2) and a further dose of ketamine (a third to half the induction dose) was administered IV in the lateral tail vein. All other animals were considered to be sufficiently immobilized (score 3) when initially approached. Statistical analysis did not reveal any differences between groups in the mean time to first signs of sedation, recumbency and approach (Table 3). Anaesthesia in the XK group was of short duration, muscle twitches were observed and animals were easily aroused by external stimuli (score 2). Anaesthesia in the MK and DMK groups was satisfactory with good muscle relaxation and no or little response to external stimuli (score 3). (Minutes) Time to first effect 4.6 ± 0.3 7.8 ± 2.2 5.8 ± 1.8 Time to recumbency 9.4 ± 2.0 11.6 ± 2.5 10.0 ± 3.2 Time to approach 15.6 ± 9.0 16.0 ± 5.0 14.8 ± 5.9 Time to sternal 39.0 ± 3.3* Time to standing 42.3 ± 3.2* One animal had not recovered by 45 minutes and was administered atipamezole so is not included in the above results. Mean times to sternal and standing in the MK and DMK group are not reported above. One animal in each of the MK and DMK groups recovered at 37 and 38 minutes after darting respectively. The remainder had not recovered by 45 minutes and were administered atipamezole. *n =9. Heart rate remained relatively stable throughout the procedure in all groups, although animals in the XK group tended to be higher at times of stimulation (Table 4). Mean HR was statistically higher in the XK group (p = 0.0001) than in the MK and DMK groups respectively but there were no differences between the MK and DMK groups (p = 0.12) (Table 4). There were no significant differences in f R between or within groups (p > 0.05). There was individual variability in body temperature but no difference between the three groups (Table 5). In each group, temperature remained within the reference interval (35 36.5 C) for this species of wallaby (England & Kock 1988; Jackson 2003). Statistical analysis of blood-gas or electrolyte values did not reveal any differences (p > 0.05) between the groups (Table 5). Forty-five minutes after darting, only one animal in the XK group required atipamezole because the anaesthesia was still deep (score 3). The remaining XK animals showed signs of recovery (lifting head and returning to sternal recumbency) after 39 ± 2 minutes and were fully recovered after 42 ± 2 minutes (Table 3). In both the MK and DMK group only one animal had recovered by the 45-minute time point: all remaining animals were still immobile and were administered atipamezole. The protocol of the study did not allow for accurate monitoring of these recoveries but all were fully recovered within 7 minutes after administration of the antagonist and no side effects were noted. 210 Ó 2010 The Authors. Journal compilation Ó 2010 Association of Veterinary Anaesthetists, 37, 207 214

Table 4 Heart rate (beats minute )1 ) and respiratory rate (breaths minute )1 ) at different times in 26 Bennett s Wallabies darted with one of three different drug combinations (Table 2) Time (minutes) 0 (time of approach) 5 10 15 20 25 HR 83 ± 27 76 ± 7 76 ± 17 92 ± 49 85 ± 39 XK 68 ± 12 71 ± 11 77 ± 25 75 ± 13 72 ± 10 74 ± 10 MK 61 ± 13 74 ± 39 65 ± 5 76 ± 46 69 ± 9 65 ± 9 DMK f R 36±13 27±8 29±7 39±18 37±25 XK 29 ± 24 26 ± 15 30 ± 10 28 ± 7 30 ± 15 33 ± 12 MK 23 ± 13 26 ± 28 27 ± 9 26 ± 3 27 ± 6 24 ± 5 DMK All results are mean ± SD. Table 5 Temperature and venous blood (sampled from the tail) parameters in 26 Bennett s Wallabies darted with one of three different drug combinations (Table 2) XK MK DMK Temperature ( C) 35.5 ± 0.1 35.1 ± 0.1 35.3 ± 0.7 ph 7.41 ± 0.00 7.40 ± 0.00 7.36 ± 0.00 PvCO 2 (kpa) (mmhg) 6.08 ± 0.14 (45.6 ± 1.8) 6.31 ± 0.20 (47.3 ± 1.5) 6.79 ± 0.41 (50.9 ± 3.1) PvO 2 (kpa) (mmhg) 9.04 ± 2.39 (68 ± 18) 8.25 ± 3.06 (62 ± 23) 7.71 ± 1.20 (58 ± 9) BEecf (mmol L )1 ) 4±1 5±1 5±5 HCO 3 (mmol L )1) 28.8 ± 0.7 29.3 ± 0.9 27.0 ± 3.7 TCO 2 (mmol L )1 ) 30±1 31±1 28±4 so 2 % 91±5 89±4 80±9 Na (mmol L )1 ) 130 ± 13 133 ± 1 135 ± 3 K (mmol L )1 ) 5.4 ± 0.02 5.4 ± 0.03 5.6 ± 0.3 ica (mmol L )1 ) 1.1 ± 0.1 1.1 ± 0. 1.1 ± 0.0 Glu (mmol L )1 ) 5.8 ± 0.4 7.6 ± 0.6 8.1 ± 0.5 PCV% 41±0 39±0 40±0 Hb (g dl )1 ) 14.1 ± 0.1 13.1 ± 0.1 13.5 ± 1.0 All data are presented as mean ± SD. Discussion Overall, all anaesthetic combinations provided sufficient sedation for the purpose of transport, venous blood sampling, treatment and clinical examination although three animals in the XK group needed a top-up dosage to achieve this level of sedation. However, arterial blood sampling, which is routinely performed at WZ to monitor the cardiorespiratory status of anaesthetized animals, was not possible in at least the XK group due to involuntary movements of the back legs and no further attempts were made in the MK and DMK groups. Although the wallabies at WZ are indifferent to people and cars, they cannot be approached. The flight distance for most animals is between 5 and 15 metres, dependent on their age and environment within the zoo, with younger animals and those inhabiting quieter areas being more nervous. Hence, successful immobilization is highly dependent on the nature of the animal, and the ability and experience of the anaesthetist in using remote darting equipment. Furthermore, knowledge about the species and their estimated body weights is crucial for successful immobilization of wildlife species. Ó 2010 The Authors. Journal compilation Ó 2010 Association of Veterinary Anaesthetists, 37, 207 214 211

Some problems were encountered during induction. Three MK animals needed a second injection for technical reasons as described above. Furthermore, three XK animals required a top-up dosage when grasping the tail. One of these weighed 21 kg and as the doses were calculated for 10 12 kg wallabies, this animal was underdosed. Poor immobilization has previously been associated with inaccurate body weight estimates in Bennett s wallabies leading to serious variability of sensitivity to xylazine ketamine dosing and large individual differences in time to recumbency as well as duration of immobilization (England & Kock 1988; Bourne 1997). Two different XK animals became excited during induction. Holz (2007) highlighted the importance of keeping macropods calm prior to and during initial induction, especially when using alpha-2 agonists, as over stimulation leads to an increased time to becoming recumbent and insufficient anaesthetic depth. Surprisingly, two animals receiving dexmedetomidine ketamine in this study were initially very excited but did not require additional anaesthetic dosing when approached. This may reflect differences between the alpha-2 agents; however, this was a too small a study in a limited number of animals to draw definitive conclusions on this aspect. Xylazine ketamine produced a much shorter anaesthetic period compared with the other two protocols, in keeping with its known shorter duration of action than medetomidine and dexmedetomidine (Lemke 2007). However, anaesthesia was considerably shorter in the present study than previously reported with xylazine/ketamine in Bennett s wallabies in WZ (England & Kock 1988). England & Kock (1988) used much higher doses of xylazine than in the current study, (mean dose 16 versus 1.63 mg kg )1 ) while ketamine doses were similar (mean dose 13 mg kg )1 versus 11.9 mg kg )1 ). This suggests that the dose of xylazine is the important factor determining the duration of anaesthesia. The dose of ketamine was higher in the XK group compared with the MK and DMK groups. In dogs, ketamine doses can be adjusted according to the required duration of anaesthesia, but in cats anaesthetized with a combination of medetomidine and ketamine, higher doses of ketamine failed to prolong anaesthesia (Lin 1996). This suggests that the high doses of ketamine used in Bennett s wallabies in the XK group might also have no or little impact on duration of anaesthesia. Furthermore, England & Kock s (1988) report showed that the group of Bennett s wallabies receiving the lowest dose of ketamine and the highest dose of xylazine had the longest duration of anaesthesia, again supporting the hypothesis that the dose rate of xylazine has more impact on duration of anaesthesia than ketamine. Animals in the XK group showed considerably more muscle contractions and reactions to external stimuli than those in the MK and DMK groups. It is most likely that the muscle contractions were a result of the well-known cataleptic side effects of ketamine. Increasing the dose of xylazine to reduce these side effects appears ineffective in Bennett s wallabies (England & Kock 1988). In contrast, animals in the medetomidine and dexmedetomidine groups did not respond to external stimuli and were still sufficiently anaesthetized 45 minutes after darting to allow the possibility of prolonged procedures in the field. In the XK group, the mean heart rate was significantly higher compared with the other two groups. Heart rate at time 0 (time of approach) was considerably higher; time 15 was at blood sampling and time 20 at microchip insertion and injections. These findings suggest the increased heart rates may have been a response to external stimuli in lightly anaesthetized animals. Furthermore, times 15 and 20 were around 30 and 35 minutes post-darting, when the effects of xylazine are likely to abate. Data for normal heart rates in conscious wallabies are contradictory. Normal heart rates in wallabies were estimated to be around 125 beats minute )1 (Burton 1962); hence all animals in this study were bradycardic. However, reference values for minimum heart rates from 63 to 86 beats minute )1 have also been reported in conscious Tammar and Rock wallabies (Bergin 1978). Wallabies anaesthetized with sodium thiopental had heart rates in excess of 110 beats minute )1 after 30 minutes (Richardson & Cullen 1981). Consequently, the results of this study indicate that all three alpha-2 agonists caused a degree of bradycardia. Respiratory rates were similar in all the groups in this study. However, particularly in the XK group, as with HR, f R increased during times of stimulation, again supporting the hypothesis that XK animals were lightly anaesthetized. Respiratory rates in unsedated Bennett s wallabies have been reported to be 30 breaths minute )1, ranging between 18 and 60 breaths minute )1 (England & Kock 1988). All f R in this study fell within this range, suggesting there 212 Ó 2010 The Authors. Journal compilation Ó 2010 Association of Veterinary Anaesthetists, 37, 207 214

was no depression in the f R in any of the groups. However, a number of animals had an initial flight reaction on impact of the dart, some animals were darted twice and other animals needed an IV top-up because of struggling when grasping the tail. All of the above might have contributed to a stress response and increased heart and respiration rates. Unfortunately, it was impossible to take any preanaesthetic or post-anaesthetic measurements so there were no conscious data for comparison. No significant differences were shown in any blood parameters between the groups in the present study. Richardson & Cullen (1981) reported arterial (mean ± SD) values for PO 2 of 82.1 ± 9.8 mmhg (10.95 ± 1.31 kpa), for PCO 2 of 36.1 ± 4.0 mmhg (4.81 ± 0.17 kpa) and for ph of 7.38 ± 0.063 in conscious wallabies. In contrast, in England & Kock s (1988) study, in wallabies immobilized for 30 minutes with xylazine and ketamine, mean arterial O 2 tensions were as low as 70 mmhg, and CO 2 tensions 50 mmhg. In this study initial attempts were made to obtain arterial samples in the XK group but due to involuntary movements of the pelvic limbs no further attempts were made. Thus the blood-gas values were determined in peripheral (tail) venous blood, and cannot be compared with those from previous studies. The electrolyte data suggest that the animals were normal with the possible exception of potassium which was slightly high. This is presumably a reflection of the excessive muscle activity that is difficult to avoid in any form of capture (Holz 2003). This study showed no differences in quality of anaesthesia (absence of muscle twitches and no reaction to external stimuli) between the medetomidine and dexmedetomidine groups. Previous studies in dogs and cats are in agreement with this concept as there were no significant differences between dexmedetomidine and medetomidine for sedation and muscle relaxation (Ansah et al. 1998; Kuusela et al. 2001). There were also no significant differences between HR, f R and body temperature in these species (Granholm et al. 2006). In this study, the dose of alpha-2 antagonist used in the DMK group was half that used in the MK group and half of the recommended dosage to antagonize dexmedetomidine in the dog (Pfizer 2007). Although detailed analyses of post-antagonist recoveries were not made, there was no noticeable difference in the time of recovery between the DMK and MK groups. This might suggest that half the dosage of atipamezole can also be used in the MK group without noticeable differences in recovery time. In conclusion, immobilization of Wallabies with the three alpha-2/ketamine-based protocols was rapid, and all combinations provided an acceptable level of sedation/anaesthesia for the purpose of the study. Although some animals needed a top-up in the XK group, recovery was shorter and did not require antagonism. Quality of restraint in the XK group was inferior to that in the MK and DMK groups. Recovery in the XK group occurred at around 40 minutes, whereas the majority of animals in the other groups were administered atipamezole to hasten recovery after 45 minutes. Bradycardia in the XK group was less severe compared with the other groups. There were no post-anaesthetic adverse effects with any of the protocols. The choice of protocol for immobilization of Bennett s wallabies at WZ will be determined by the procedure. When a short period of restraint is required simply to transport an animal, carry out a health check and collect a blood sample, xylazine ketamine will be acceptable, especially because the cardiovascular side effects are less pronounced and recovery is faster. When a prolonged procedure is necessary medetomidine or dexmedetomidine and ketamine would be more appropriate. Acknowledgements The authors would like to thank Jo Dodds for helping in the animal captures, the keepers at ZSL Whipsnade Zoo for looking after the animals after capture, Aviva Petrie for the assistance with the statistics and Pfizer Animal Health, UK for providing Dexdomitor. References Ansah OB, Raekallio M, Vainio O (1998) Comparison of three doses of dexmedetomidine with medetomidine in cats following intramuscular administration. J Vet Pharmacol Ther 21, 380 387. Bergin TJ (1978) Marsupials and monotremes; Physiology. In: Zoo and Wild Animal Medicine. Fowler ME (ed.). WB Saunders Company, Philadelphia, Philadelphia, USA. pp. 401 404. Boever WJ, Stuppy D, Kane KK (1977) Clinical experience with tilazol TM (CI744) as a new agent for chemical restraint and anesthesia in the red kangaroo (Macropus rufus). J Zoo An Med 8, 14 17. Bourne DC (1997). Disease and mortality in Bennett s wallabies (Macropus rufogriseus rufogriseus) at Whips- Ó 2010 The Authors. Journal compilation Ó 2010 Association of Veterinary Anaesthetists, 37, 207 214 213

nade Wild Animal Park, with special reference to toxoplasmosis. PhD thesis, Institute of Zoology & Royal Veterinary College, London, UK. Burton M (1962) Order Marsupialia (Marsupials). In: Systematic Dictionary of Mammals of the World. Burton M (ed.). Museum Press Limited, London, UK. pp. 26 37. Cole JR, Langford DG, Gibson DF (1994) Capture myopathy in Lagorchestes hirsutus (Marsupialia: macropdidae). Aust Mammal 17, 137 138. England GC, Kock RA (1988) The use of two mixtures of ketamine and xylazine to immobilize free ranging Bennett s wallabies. Vet Rec 122, 11 14. Granholm M, McKusick BC, Westerholm FC et al. (2006) Evaluation of the clinical efficacy and safety of dexmedetomidine or medetomidine in cats and their reversal with atipamezole. Vet Anaesth Analg 33, 214 223. Holz P (2003) Marsupialia (Marsupials). In: Zoo & Wild animal medicine (5th edn). Fowler ME, Miller RE (eds). Elsevier Science, Missouri, USA. pp. 288 303. Holz P (2005) Restraint and Anaesthesia of Macropods. In: Zoological Restraint and Anaesthesia. Heard D (ed.). http://www.ivis.org/special_books/heard/holz6/chapter.asp?la=1 (accessed on 25 November 2009). Holz P (2007) Marsupials. In: Zoo Animal and wildlife Immobilisation and Anaesthesia. West G, Heard D, Caulkett N (eds). Blackwell Publishing, Ames, IA, USA. pp. 341 346. Jackson S (2003) Macropods. In: Australian mammals Biology & Captive Management. Jackson S (ed). CSIRO Publishing, Collingswood, Australia. pp. 246 296. Jalanka HH, Roeken BO (1990) The use of medetomidine, medetomidine-ketamine combinations, and atipamezole in nondomestic mammals: a review. J Zoo Wildl Med 21, 259 282. Kuusela E, Vainio O, Kaistinen A et al. (2001) Sedative, analgesic, and cardiovascular effects of levomedetomidine alone and in combinations with dexmedetomidine in dogs. Am J Vet Res 62, 616 621. Lemke KA (2007) Anticholinergics and sedatives. In: Lumb & Jones Veterinary Anesthesia and Analgesia (4th edn).tranquilli WJ, Thurmon JC, Grimm KA (eds). Blackwell Publishing, Ames, IA, USA. pp. 203 239. Lin HC (1996) Dessociative anesthetics In: Lumb & Jones Veterinary Anesthesia and Analgesia (3rd edn). Thurmon JC, Tranquilli WJ, Benson GJ (eds.). Williams & Wilkins, Baltimore, MD, USA. pp. 241 296. Pfizer (2007) Antisedan. Summary of product charachteristics. http://www.vmd.gov.uk/productinformation Database/Documents/138469.doc. (accessed on 25 November 2009). Pye GW, Booth RJ (1998) Medetomidine-ketamine immobilization and atipamezole reversal of Eastern grey kangaroos (Macropus giganteus). Proceedings of the AAZV and AAWV Joint Conference, Omaha, Nebraska, USA. pp 306 309. Richardson KC, Cullen LK (1981) Anesthesia of small kangaroos. J Am Vet Med Assoc 179, 1162 1165. Richardson KC, Cullen LK (1984) Physical and chemical restraint of small macropods. In: International Zoo Yearbook 23. Olney PJS (ed). The Zoological Society London, London, UK. pp. 215 218. Shima AL, McCracken H, Lynch MJ (1993) Use of tiletamine-zolazepam in the immobilization of marsupials. Proceedings of the American Association of Zoo Veterinarians, Saint Louis, MO, USA. pp 171 174. Unwin S (2004) Physical and anaesthetic restraint of macropods, koalas and cassowaries some practical tips. Proceedings of the European Association of Zooand Wildlife Veterinarians (EAZWV), Ebeltoft, Denmark. pp. 159 165. Received 22 July 2009; accepted 7 October 2009. 214 Ó 2010 The Authors. Journal compilation Ó 2010 Association of Veterinary Anaesthetists, 37, 207 214