Restraint and Anesthesia of Macropods

Introduction

Macropods are kangaroos, wallabies and their relatives (Table 1). All have powerful hindlimbs and long hindfeet. The fourth toe on the hindfoot is the longest and strongest and bears the full weight of the animal while hopping. The second and third toes are fused (syndactyly) except at the tip where two separate claws protrude.

Only one pair of incisors is present in the lower jaw and there are three pairs of upper incisors. Macropods are predominantly herbivorous being either browsers or grazers. Potoroos will also consume fungi, seeds and insects.

All macropods have a well-developed forward opening pouch that contains four teats. Usually one young is born at a time. Females experience a postpartum estrus. If fertilization occurs, the embryo remains as a blastocyst in embryonic diapause; the western grey kangaroo (Macropus fuliginosus) is an exception to this rule. Diapause is maintained by the sucking stimulus of the pouch young. If the pouch young dies or vacates the pouch development continues. Once leaving the pouch the young macropod continues to suckle for a time before being weaned. Consequently the younger sibling must feed from one of the three remaining teats, which produces milk of a different composition to that being consumed by the older animal.

Manual Restraint

Manual restraint is only used for minor procedures or prior to the induction of general anesthesia. Any attempt at physical restraint will result in considerable panic and struggling on the part of the animal that will activate the "fight or flight response". This will lead to a release of catecholamines that may result in untoward effects such as hyperthermia, exertional rhabdomyolysis and ventricular fibrillation.

As well as attempting to escape, the animal will try to defend itself. Macropods will endeavour to kick the individual attempting to restrain them. Due to the size of the claw on digit four and the powerful hindlimb muscles this can result in serious injury to the handler. Macropods will also bite and can inflict painful injuries with their teeth. Large kangaroos should never be manually restrained, as their hindlegs cannot be adequately controlled. Chemical restraint is strongly recommended.

Wallabies and smaller macropods can be caught in a net. Care is required with exhibit design, since macropods will tend to run close to the fence when pursued. All poles and supporting structures must be outside the pen. The inside wall of the pen must be smooth with no protuberances. As with animal care, patience and quiet are required. Many species panic easily and may collide head on with the fence resulting in soft tissue trauma and cervical fractures.

Once caught in a net, the macropod can be grasped at the base of the tail and lowered into a Hessian (Burlap) sack or pillowcase, depending on the size of the animal. Animals in bags tend to relax as outside stimuli and visual threats are removed. The chance of injury is decreased, since they cannot kick out against solid objects. It also gives the operator the upper hand as they know where the animal is but the animal does not know where the operator is. It is important not to hold the bag against the handler’s body while the animal is being transported. They can still kick or bite through the bag injuring the handler.

If restraint and examination of the conscious macropod is required medium sized wallabies can be held by the tail and grasped between the thighs. The handler’s legs hold the wallaby around the abdomen cranial to the pelvis. Tail and hindlegs are then held. It is important to hold the hindlegs above the hock. Otherwise, if the animal kicks out, it may break a leg. If the legs are being held with one hand, place a digit between the legs to prevent injury. The animal can then be examined.

If more handlers are available one person grasps the tail base while a second person grasps the animal firmly behind the head. It is important to approach the animal from the dorsal aspect to avoid the hindlimbs. A third operator may be required to restrain the hindlegs.

It is important to emphasize that animals restrained in this way, unless they are tame or hand raised, will be extremely stressed and struggle vigorously against the restraint. It should only be used for short term procedures or as a prelude to chemical restraint.

Figure 1. Manual restraint of a rufous bettong (Aepyprymnus rufescens). Note firm grasp behind the head to prevent biting and restraint of hindlegs.

Chemical Restraint - Inhalant Anesthesia

Inhalation anesthesia is the technique of choice. If the animal weighs <10 kg, and can be manually restrained, the safest way to induce general anesthesia is via a non-rebreathing circuit (e.g., Ayre's T-piece) and a mask. Animals >10 kg should be maintained on a rebreathing system (e.g., Circle). Masks can be custom made using variably sized plastic bottles. The bottom is cut off and a piece of rubber glove is stretched over the opening. A hole is then made in the glove to accommodate the animal's face. For animals in bags anesthesia is induced by extracting the macropod’s head and placing the face in the mask. In this way the operator is protected to some extent from the powerful hindlimbs as they are contained within the bag.

On a non-rebreathing circuit induction involves exposure to 5% isoflurane delivered at an oxygen flow rate of 200 ml/kg/min with a minimum of 1L/min. For a rebreathing circuit, oxygen flow rate should be 50 ml/kg/min. Maintenance of anesthesia generally requires 2% isoflurane, but this varies between species and individuals.

If isoflurane is unavailable halothane is an acceptable substitute, but is not as safe and requires close monitoring.

For prolonged procedures macropods should be intubated as they may regurgitate. Intubation is difficult as they have a narrow oral cavity and small gape. However, if the neck is extended and a long straight bladed laryngoscope is used it is possible to visualise the larynx. An endotracheal tube can then be passed. Generally the larynx is smaller than would be expected for an animal of that size.

Chemical Restraint - Injectable Anesthesia

If the animal cannot be restrained to induce gaseous anesthesia, it will require an injectable induction. Sedation suitable for transport will occur five to twenty minutes after 1 - 2 mg/kg diazepam is injected intramuscularly (IM). Duration of effect is approximately one to two hours. Azaperone has been used at 2 mg/kg IM. Effects appear after 15 to 20 minutes and last for 3 - 8 hours.

To induce general anesthesia Zoletil (Telazol) 10 mg/kg can be injected IM [9]. Zoletil is a combination of tiletamine and zolazepam. The advantage of Zoletil is its low volume and rapid effect, making it ideal for remote capture by dart (Fig. 2). However, relaxation is variable and salivation may be excessive. This can be controlled with 0.04 mg/kg atropine. Recoveries can also be prolonged (1 to 5 hours).

Figure 2. Remote immobilisation. Note placement of dart in major muscle mass.

Alternatively, ketamine can be combined with an α2 agonist and injected IM. Ketamine 10 to 25 mg/kg mixed with xylazine 5 mg/kg, will provide satisfactory immobilisation but the large volume required precludes its use in bigger macropods. Ketamine combined with medetomidine provides superior relaxation to Zoletil and, if the concentrated medetomidine solution (10 mg/ml, Zalopine) is used, only requires a small volume. It is, however, extremely expensive. Induction times are longer than with Zoletil, up to 20 minutes, and it is important not to stimulate the animal during induction as this will extend the time to recumbency or result in inadequate immobilisation.

Published dose rates for ketamine/medetomidine combinations in macropods are ketamine 2 - 3 mg/kg and medetomidine 50 - 100 μg/kg [7], ketamine 2 - 3 mg/kg and medetomidine 40 - 80 μg/kg [9], ketamine 4 mg/kg and medetomidine 40 μg/kg [6]. The author can recommend a dose of ketamine 5 mg/kg combined with medetomidine 50 μg/kg for red kangaroos (Macropus rufus) and western grey kangaroos. However, these dose rates are too low to induce effective immobilisation in eastern grey kangaroos (Macropus giganteus). Relaxation in this species was improved using a combined dose of 5 mg/kg ketamine and 125 μg/kg medetomidine but results were too erratic to recommend this regime. The 5 mg/kg ketamine/125 μg/kg medetomidine dose quoted above also proved inadequate to restrain smaller macropods such as pademelons and parma wallabies (Macropus parma).

Ketamine/medetomidine immobilisation can be reversed using intramuscular or subcutaneous atipamezole administered at five times the dose of medetomidine. The author has successfully used this dose intravenously with no adverse effects. Animals are standing, but still ataxic, approximately 10 to 20 minutes after reversal.

Zoletil 3 - 5 mg/kg has been combined with xylazine 0.5 - 2.0 mg/kg and reversed with yohimbine at 0.2 mg/kg IV. This combination does not appear to confer any advantages over those listed above.

Many macropod species are quite highly strung and may benefit from the use of long acting tranquilisers when settling into new exhibits. The author has successfully used a combination of zuclopenthixol decanoate (Clopixol) and pipotiazine palmitate (Piportil) at 10 mg/kg of each drug administered intramuscularly to red-necked wallabies (Macropus rufogriseus). This dose is much higher than that recommended for hoofstock but lower doses proved ineffective. Duration of effect was approximately 10 days [3]. Fluphenazine decanoate (Modecate) 2.5 mg/kg IM has also been recommended [9]. Duration of effect was approximately 7 days. In the author’s experience fluphenazine produced no appreciable effect at this dose when used in red kangaroos and eastern grey kangaroos. Higher doses may be required.

Venipuncture Sites

Lateral coccygeal vein - A large vein is present on both lateral aspects of the tail (Fig. 3a). Applying pressure or a tourniquet to the tail base will raise the vein (Fig. 3b).

Medial saphenous vein - This is a small vein coursing along the medial aspect of the hindleg.

Cephalic vein - This vein is present on the dorsal surface of either foreleg.

Jugular vein - This vein is suitable for blood sampling in all macropods (Fig. 4).

Ventral coccygeal vein/artery complex? The author uses this route routinely for the macropods he attends to.

Figure 3a. Lateral coccygeal vein in an eastern grey kangaroo.

Figure 3b. Lateral coccygeal vein. Applying pressure or a tourniquet to the tail base will raise the vein.

Figure 4. Jugular vein in an eastern grey kangaroo.

Table 2 and Table 3 list published hematology and biochemistry values for some macropod species.