Abstract
As part of a chamois (Rupicapra rupicapra) monitoring project in the National Park Berchteagaden an immobilization protocol using a combination of 65 µg/kg medetomidine and 1.5 mg/kg ketamine and its subsequent reversal with 0.4 mg/kg atipamezole has been used. Immobilization was induced with a modified CO2 dart gun that allowed application distances of up to 80 m. In our view this method seems to be a viable time-saving alternative to more traditional trapping methods. The use of a specific antagonist allows for very individual anesthesia configuration and safe release in the steepest alpine environment.
Introduction
Free-ranging chamois in the past have been captured using various leg snares and box traps.1,6 These methods have some important disadvantages. Use of snares in the winter increases the risk of digital frostbite and boxtraps are prone to mechanical defects caused by icing up of the various triggers.5 Both snares and boxtraps require a lot of manpower for constant monitoring purposes. Both methods are also highly “visible” and could have had a negative impact on the large numbers of visiting tourists.
Methods
Because of these disadvantages it was decided to rely on chemical immobilization applied by a CO2 dart gun. After hardware testing, came up with the following combination was developed. A high-pressure CO2 dartgun (Daninject IM 25 bar, Smith GmbH, Gelsenkixchen, Germany) and low weight single use 1 cc plastic-aluminum darts with barb (Pneudart, Williamsport, PA, USA). Accurate determination of the shooting distance is of utmost importance and, therefore, a scope with integrated laser distance measurement (Swarovski LRS, Abaam/Tirol, Austria) was used. Extensive testing in the pre-project phase allowed us to reduce the impact velocity and, therefore, allow for dart hits on practically the entire body and thus minimize the danger of trauma due to dart impact. The reduction of the impact velocity, however, goes hand-in-hand with a decrease in the accuracy of the system due to the greater curve of the dart and its lower speed.
The basic requirements postulated for the chemical immobilization were an extremely rapid and smooth induction (short flight distance), a small drug volume (longer possible dart trajectories), good sedation and muscle relaxation (better manipulation) and an antagonist (allows for shorter downtime and reversal of the drug effects should a problem arise). Various chemical immobilization techniques for chamois are described in the literature. One of the most frequently used methods is the use of the “Hellabrunnar mixture” (125 mg xylazine + 100 mg ketamine/ml). This combination allows a good immobilization using a very small drug volume (0.04–0.08 ml).13 Other combinations that have been used are etorphine-acepromazine14 and tiletamine-zolazepam.4
The pioneering work of Jalanka7-11 with medetomidine, ketamine, and atipamezole has added a very useful supplementary drug combination to the zoo and wildlife immobilization palette. In the past years this combination has been tested on a large number of exotic species.2,3 Medetomidine is an alpha-2 adrenergic agonist similar to the frequently used xylazine and the more recently developed detomidine. Its action is characterized by a dose dependent sedation to anesthesia, good muscle relaxation and analgesia. The main side effects are a marked bradycardia with subsequent hypotension and hypothermia. More detailed descriptions of the pharmacological and physiological properties of medetomidine and atipamezole have been reported.2,7,8 Though an immobilization is possible using medetomidine alone, Jalanka and Roken had recommended its use in combination with low doses of ketamine.7 Medetomidine is available in the European market in two concentrations: 1 mg/ml (Dormitor Farmos, Turku, Finland) and 10 mg/ml (Zalopine Farmos Turku, Finland). The alpha-2 adrenergic antagonist atipamezole is available at 5 mg/ml (Antisedan Farmos, Turku, Finland). Using the work of Jalanka and Roeken7 and Berthier3 and a pre-field test12 as a basis, the field work was started using an estimated initial dose of 70 µg/kg medetomidine and 1.5 mg/kg ketamine. Anesthesia was monitored in the field using sequential rectal temperature measurements, heart rate and oxygen saturation with a pulsoximeter (Nellcor NP-20).
Results
Medetomidine was used in an average dose of 65 µg/kg and ketamine at a dose of 1.5 mg/kg. As an antagonist, atipamezole was used intravenously at an average dose of 0.4 mg/kg was used. In all cases reversal using atipamezole was calm, complete and extremely rapid (<2 minutes). Induction time to lateral recumbency is dependent on accurate body weight estimation. Underestimation of body weights later in the capture season due to increased weight gain of animals in the summer caused some problems. When the weight estimation was fairly accurate and the animal could be observed, induction time was extremely short (4–6 minutes). To date, it has been possible to successfully dart and collar 11 individuals (4.7). A total of 16 direct hits were recorded with an average application distance of 65 m (range 3–85 m). Five animals could not be found post application (darkness, dense forest) and one animal had to be killed after a headlong fall. An average of 25 hours work per animal captured has been necessary.
Discussion
After the first capture season this method seems to be a viable time-saving alternative to more traditional trapping methods. During pre-immobilization, special attention must be given to the geographical location (avoidance of rock faces and precipices) and ample consideration to the problems of animal recovery post induction (use of hunting dog, etc.). The use of a specific antagonist allows for very individual anesthesia configuration and safe release in the steepest alpine environment.
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