Restraint and Anesthesia of Dasyurids (Dasyuromorphia)

Introduction

Dasyurids represent the carnivorous marsupials that range in size from the narrow-nosed planigale (4 - 9 g) up to the Tasmanian devil (up to 9 kg). Table 1 lists all the dasyurids with their weights. They have four pairs of upper incisors, three pairs of lower incisors, well developed upper and lower canines, two or three pairs of upper and lower blade-like premolars and four pairs of upper and lower molars with sharp, shearing cusps. The forefeet have five clawed toes, the first toe on the hindfoot is either short or absent, and the second and third toes of the hindfeet are not fused. This fusion is seen in many of the other marsupial groups, such as the macropods and possums.

The number of teats ranges from four to twelve. Many species lack a pouch. In phascogales eight teats are situated on a circular patch of skin on the abdomen. In other species low lateral folds develop at the sides of the mammary area of a lactating female. These folds do not constitute a pouch in the strict sense and provide very little protection for the young which, as they develop, dangle from the mother’s belly between her fore- and hindlegs. A permanent pouch is present in most ningauis, kultarr, spotted-tail quoll and Tasmanian devil.

Manual Restraint

Wild animals perceive handling as a major stressor usually associated with being killed. Consequently, manual restraint is only used for minor procedures or prior to the induction of general anaesthesia. Any attempt at physical restraint will result in considerable panic and struggling on the part of the animal which will activate the "fight or flight response". This will lead to a release of catecholamines that may result in untoward effects such as hyperthermia or ventricular fibrillation.

As well as attempting to escape the animal will try to defend itself. In the case of dasyurids they will endeavour to bite the individual attempting to restrain them. This will result in a minor degree of pain and inconvenience when caused by an antechinus or dunnart, but the larger members of the group, such as the Tasmanian devil, can inflict severe injuries. Considerable care is required when attempting to restrain this last group.

When restraining or transporting dasyurids it is advantageous to place them in a bag. This can range from a pillowcase in the smaller animals up to a large Hessian (Burlap) sack for Tasmanian devils. Animals in bags tend to relax as outside stimuli and visual threats are removed. The chance of injury is decreased, as 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.

Small dasyurids can be gripped by the scruff of the neck and placed in a bag. Alternatively, they can be held firmly around the body (Fig. 1). It is important not to clasp them too firmly as suffocation is possible.

Larger dasyurids, such as quolls and devils, can be caught in a net or restrained by the tail and then lowered into a bag. Devils must be closely monitored while in the bag as they can chew their way out.

Figure 1. Manual restraint of an eastern quoll.

Chemical Restraint - Gaseous Anaesthesia

This is the anaesthetic technique of choice. If the animal can be manually restrained, the safest way to induce general anaesthesia is via a non-rebreathing circuit (e.g., Ayre's T-piece), and a mask (Fig. 2). 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 anaesthesia can be induced either through the bag, or by extracting the head and placing it in the mask.

Induction involves exposure to 5% isoflurane delivered at an oxygen flow rate of 200 ml/kg/min with a minimum of 1L/min. Maintenance of anaesthesia 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.

Figure 2. Tasmanian devil maintained an isoflurane with a facemask.

Chemical Restraint - Injectable Anaesthesia

If the animal cannot be restrained to induce gaseous anaesthesia it will require an injectable induction. Sedation suitable for transport will occur after 1 - 2 mg/kg diazepam is injected intramuscularly.

To induce general anaesthesia Zoletil (Telazol) can be injected at 10 mg/kg intramuscularly [1]. Zoletil is a combination of tiletamine and zolazepam. The advantage of Zoletil is its low volume and rapid effect. However, relaxation is variable, constant limb movement having been observed in Tasmanian devils. Recoveries can also be prolonged, in excess of six hours in one Tasmanian devil [2]. Alternatively, xylazine/ketamine combinations can be used. Dose rates are 4 mg/kg xylazine combined with 20 mg/kg ketamine injected intramuscularly.

Venipuncture Sites

Ventral coccygeal vein - Insert the needle perpendicular to the tail, in the ventral midline, and advance it until the vertebrae are reached. Withdraw the needle slightly and blood should enter the needle hub. This vein is useful for smaller dasyurids (Fig. 3).

Femoral vein/artery - Direct the needle at the pulse felt in the groin region. Arterial blood is often obtained and digital pressure is required to prevent hematoma formation.

Medial metatarsal vein - This is a small vein running along the medial aspect of the hindleg.

Cephalic vein - This vein is present on the dorsal surface of either foreleg. It can be used in Tasmanian devils and quolls.

Jugular vein - This vein is suitable for blood sampling in all dasyurids.

Figure 3. Ventral coccygeal vein in an antechinus.

Tables 2 - 4 list published physiological parameters, and hematology and biochemistry values for some dasyurid species.