Abstract

Diazepam followed by succinylcholine chloride was administered intramuscularly to 26 healthy mature female alligators on two occasions. The mean diazepam dosage was 0.37 mg/kg (0.28 mg/kg to 0.62 rng/kg) and the mean succinylcholine chloride dosage was 0.24 mg/kg (0.14 mg/kg to 0.37 mq/kg). This drug combination reduced stress and allowed adequate immobilization for restraint and handling. The reduced drug volume, low dosage of succinylcholine chloride required, short induction period, maintenance of respiration, and adequate degree of immobilization make this drug combination a good alternative to the use of muscle relaxants alone in the chemical restraint of alligators.

Introduction

The University of Florida in cooperation with Gatorland Zoo of Kissimmee, Florida is studying artificial insemination in the American alligator (Alligator mississippiensis).

Physical restraint of the animals produced stress and appeared to reduce the number of animals which ovulate and subsequently lay. Diazepam (Valium, Roche Laboratories, Nutley, N.J.), in combination with succinylcholine chloride (Sucostrin, Squib, Princeton, N.J.), was used intramuscularly in the present report to reduce the animals' awareness of its environment and for chemical immobilization to facilitate handling for cloaca examination and artificial insemination. Since using this method of chemical restraint, some animals have been examined as many as five times in one month and still ovulate and lay. Physical restraint alone causes considerable stress and risk of injuries to crocodilians and/or their handlers; thus, pretreatment with diazepam followed by administration of succinylcholine chloride for immobilization is desirable.

The use of succinylcholine chloride has been reported in saltwater crocodiles (Crocodylus porosus) and freshwater crocodiles (C. johnsoni) , but premedication with diazepam was not used to reduce stress and the dose of succinylcholine chloride required for immobilization was higher than that used in this study (1). Brisbin administered succinylcholine chloride alone to nine juvenile alligators weighing between two and five kg and found this produced a completely relaxed state at dosages ranging from 0.46 mg/kg to 2.25 mg/kg (2). The use of ketamine, pentobarbital, nicotine, etorphine, d-tubocurarine, and gallamine in crocodilians has been previously reported with varying degrees of success (2,4,5,6,7).

Materials and Methods

Twenty-six female alligators of breeding age, weighing between 40 and 106 kg, were maintained in individual pens; each containing a small pool, as well as a dry land environment. The pools could he drained for cleaning, as well as for performing procedures requiring physical or chemical restraint. On two occasions (April 30, 1982 and May 13, 1982), immobilization and artificial insemination procedures were carried out on each female. The study was performed over a 12 hour period on the two occasions. The ambient temperature varied from 21 to 26 C on April 30, 1982 and from 23 to 28 C an May 13, 1982. The weights of the animals were initially estimated and the true weights determined following immobilization. The diazepam dose was administered intramuscularly in the hind limb using a pole syringe at a mean dosage rate of 0.37 mg/kg (range = 0.28 to 0.62 mg/kg). Twenty minutes later, succinylcholine chloride was administered intramuscularly at a mean dosage rate of 0.24 mg/kg (range = 0.14 mg/kg to 0.37 mg/kg).

Successful immobilization was defined, for the purposes of this study, as the ability of the handler to walk up to the alligator and tape the mouth shut with electrician's tape. The animal was then carried to the study site for performance of the necessary invasive reproductive arid monitoring procedures. The animals were weighed following immobilization. Electrocardiography (EK-5A Electrocardiograph, Burdick Corporation, Milton, WI) or ultrasonography (Ekolife, SmithKline Instruments, Sunnyvale, CA) was used for determination of heart rate. Observations of the external nares flap was used as an indirect indicator of respiratory rate. Palpebral reflexes were noted when periorbital stimulus was applied.

Results

Within 20 minutes of administration of the diazepam, the animals' aggressiveness was markedly decreased; the animal would still strike at a pole, though with a much slower response time. Limb posture was still normal at this point in the procedure. Within 5-15 minutes of administration of the succinylcholine chloride, the animals did not respond to the pole and were approachable for taping of the mouth. The hind limb posture was generally unchanged, but the front limbs were generally spread wide and the digits were no longer in contact with the ground. The axial musculature of some animals was noted to twitch transiently within 5 minutes of injection of the succinylcholine chloride. When the diazepam and succinylcholine chloride combination reached maximum effect approximately 15 minutes after the succinylcholine chloride dose, the head was seen to be markedly deviated laterally. This response to the succinylcholine chloride was also noted by Messel (1). Palpebral reflexes were depressed or absent in all animals for at least 2 hours following succinylcholine chloride administration. The animals were placed in a dry shaded area for recovery and observed until respiratory rates began to increase. Heart rates during the immobilization procedures ranged from 8 to 60 beats per minute (mean = 43.5) and the respiratory rate ranged from 1 to 32 breaths per minute (mean = 13.2).

Within two to three hours following return to their pens, the animals began to show more rapid palpebral reflexes, increased response to external stimuli, and more appropriate limb posture and movement. The pools in the individual pens were filled the following morning and all animals were observed to be functioning and eating normally.

No short or long term side effects to the drug combination were noted on these two occasions. Recovery was, in general, rapid--indicated by the return of rapid eye blink reflexes, hissing, and threatening open mouth behavior. Some responded in this manner within two to three hours, while others required longer periods.

All 26 animals were adequately immobilized on the two occasions using the injectable drug combination. In three of the animals, additional physical restraint was accomplished by strapping the animal to an aluminum ladder to restrict limb and tail movement. In these animals, a righting reflex was present even with the drugs administered.

The dosage range used in these animals was 0.31 mg/kg to 0.46 mg/kg for Diazepam and 0.21 mg/kg to 0.34 mg/kg for succinylcholine chloride. In 12 other instances, lower doses of each drug completely immobilized the animals with no additional physical restraint.

Discussion

Premedicating the animals with Diazepam followed by the use of succinylcholine chloride at the dosages listed was successful for immobilization in 53 of 56 restraint procedures in 26 animals on two occasions. Compared to physical restraint alone, it was found that the muscle relaxation in the cloacal region facilitated examination for reproductive procedures. Premedication with diazepam reduced the animals awareness and allowed the use of a lower dose of succinylcholine chloride than that previously reported in the literature (1,2). The animals continued to respire during immobilization; thus, the use of diazepam probably reduces or eliminates any psychic trauma associated with loss of voluntary respiratory control associated with the use of succinylcholine chloride alone.

The use of this method of immobilization does not appear to be detrimental to reproductive performance, since 3 of the 26 animals layed fertile clutches which subsequently produced live young. The previous season, 1 animal successfully produced fertile eggs. These 4 clutches of successful live births are the only ones reported in the alligator using artificial insemination techniques.

Although in the 1982 trial of this drug combination no adverse affects were noted, there was one death in April 1983 and one death in April 1984 in the same group of animals using the same techniques and dosages. The cause of death in those animals is not known at this time, but it is believed that respiratory arrest may have contributed to the animals death (5). It would be prudent to have respiratory support devices available.

All handling of the animals was done in drained pens. This report makes no statement on the use of this drug combination in a field situation, since it is not known how an animal may respond in an aquatic environment when heavily tranquilized. Procedures more stressful than artificial insemination or which are painful would require the use of anesthetic agents which provide an adequate degree of analgesia.

Acknowledgements

The authors wish to thank Frank Godwin, Gatorland Zoo, Kissimmee, FL and the Florida Alligator Farmers Association for assistance and partial support. This manuscript has been accepted for publication in the Journal of the American Veterinary Medical Association, Wildlife issue (December, 1984).

References

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