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Anaesthesia in Pygmy Lorises Nycticebus pygmaeus

By Ulrike Streicher, Endangered Primate Rescue Center, Vietnam
2 March 2002

Pygmy lorises are most commonly anaesthetized with ketamine, tiletamine/zolazepam or isoflurane. The two latter ones are not available for the rescue center so initially a ketamine/xylazine mixture was used. At San Diego Zoo the average ketamine dosage used for pygmy lorises is 8-12mg/kg (Sutherland-Smith et al., 2000), other authors suggest dosages from 5mg (Gass, 1978) up to 20mg (Goeltenboth et al., 1990) per kg bodyweight. Wiens (1995) reports having successfully anaesthetized slow lorises with dosages between 11.3 and 33.3mg/kg

The first animal was injected with 4mg ketamine and 2mg xylazine intramuscularly. Six minutes later it was sitting in the same position but was insensitive to the touch. It was still able to move but only very slow though it was given another 2mg of ketamine and 1 mg of xylazine. After another five minutes the animal was asleep. The eyes remained half open and there was no relaxation of the muscles the animal was completely stiff. The animal was measured, given an intrapalpebral Tb-test, photographed and a microchip was implanted. The animal started to come round 64 minutes after the first injection. During anaesthesia the animal showed a high respiration frequency with 160 breaths per minute and had a heart rate of 92 beats per minute. The body temperature was not measurable so it must have been below 33°C what was the measuring range of the used thermometer. Unfortunately the temperature had not been taken before the animal was put under anaesthesia so it was possible to tell how much this low body temperature was influenced by the xylazine. The environmental temperature was 20°C with strong wind and light rain.

The animal was put in its sleeping box and the cage was covered with a blanket to protect the animal against the wind in case it would leave the sleeping box. The following morning the animal was back to normal, it had been feeding during the night and instead of staying inside the sleeping box it was sleeping in its preferred sleeping site in the branches.

A second animal was injected with 5 mg of ketamine. After ten minutes there was still no sufficient anaesthetic effect achieved, so the animal was injected with another 4 mg of ketamine. After another six minutes the animal was asleep. The respiration rate was 108 breaths per minute and the heart rate was 142 beats per minute. The body temperature was 34.6°C with the environmental temperature being 24°C and the weather being sunny and dry. The animal came round 40 minutes after the first injection.

How much the difference in the body temperature in these two cases was influenced by the use of xylazine cannot be assessed. But due to the circulation depressive side effects and the negative influence on the body temperature the use of xylazine might be problematic in a hypo metabolic prosimian.

Based on these first experiences anaesthesia was then routinely performed solely using ketamine (Ursotamin®) and an overview over the used dosages and some basic values are shown in table 1.
 

Table 1

 
Dosage in mg Weight in g Sex Teffective in minutes Trecovery in minutes Heart rate in beats/minute Respiration rate in Breaths/minute Tbody in °C
9* 550 M 16 40 142 108 34.6
6 300 M 5 53 92 52 -
12* 580 F 10 40 100 76 35.3
6 310 M 6 27 68 40 34.1
15 580 F 10 47 156 144 -
12* 360 F 13 28 76 92 34.9
7 360 F 10 38 94 132 33.6
7 240 M 9 34 92 104 -
24* 400 M 27 57 92 140 34.0
10 400 M 8 25 84 130 34.5
7 400 M 5 28 186 124 34.8
7 400 M 5 26 172 84 -
10 440 M 6 26 200 160 35.1
8 360 F 7 39 148 160 35.1
7 420 M 6 30 142 96 35.1
8 380 F 4 28 160 126 36.5
8 480 F 7 32 140 126 36.5
8 340 F 4 36 156 158 36.8
8 330 F 5 40 184 126 36.7
10 260 M 5 45 154 52 35.1
10 300 F 3 46 144 74 36.2
20* 320 M 15 45 198 40 36.2
10 400 M 4 25 176 144 34.9
6 320 F 5 25 180 146 34.3
In the *marked cases the initial dosage had only an insufficient effect and repeated injections were necessary. In these cases Teffective gives the time from the first injection until a sufficient depth of anaesthesia was achieved.

Result

Ketamine has proofed to be a suitable anaesthesic drug for routine checks and smaller painless procedures for example to fix a radio collar or  implant a microchip. A total number of 24 pygmy lorises have been anaesthetized using an average dosage of mg/100g bodyweight. Anaesthesia was only performed during the late afternoon hours taken into respect the lorises’ nocturnal activity pattern. Furthermore anaesthesia was avoided during the animals resting period in winter. Animals were injected in the cages without too much handling, e.g. in their sleeping boxes or by being fixed with one hand in their present position and then left in the cage. The effect was achieved after few minutes and the animals could then be taken out without unnecessary struggling (clinging to furniture and wire). Anaesthesia lasted sufficiently long for smaller procedures. The animals were seemingly still sensitive to noise and special care was taken to avoid any disturbing influences during anaesthesia. There was surprising variation in the heart and respiration rates, which cannot clearly been drawn back to the state of excitement prior to anaesthesia.

References:

Sutherland-Smith, M., Stalis, I.. 2001. Review of Loris Clinical information and Pathological Data From The San Diego Zoo:1982-1995. In: Management of Lorises in Captivity. A Husbandry Manual for Asian Lorisines (Nycticebus & Loris ssp.). Fitch-Snyder, H. and Schulze, H. (eds.). 2001. Center for Reproduction in Endangered Species (CRES), Zoological Society of San Diego, USA

Gass, H., 1987: Affen. Pp. 1-43 in: Krankheiten der Wildtiere, Gabrisch, K.; Zwart, P. (eds.), Schlütersche , Hannover. (German)

Goeltenboth, R.; Kloes, H.-G., 1995. Krankheiten der Zoo-und Wildtiere. Blackwell Wissenschaftsverlag, Berlin.

Wiens, F., 1995. Verhaltensbeobachtungen am Plumplori Nycticebus coucang (Primates: Lorisidae) im Freiland. Diplomarbeit. Johann Wolfgang Goethe-Universitaet, Frankfurt a.M., Germany
 
 

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