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This article was published in 1964
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Anaesthesia and Restraint in Wild Animals
L. H. LARSEN, B.V.Sc., M.S., Ph.D. Associate Professor in Veterinary Surgery, University of Sydney.
In Europe and America and more recently in Australia, there has been a growing appreciation of the role of the veterinarian in the control and care of wild animals. The capture of these animals in the field by means of drugs is rapidly replacing earlier methods, while in zoological gardens the transport of animals or their capture for treatment, using tranquillisers and relaxants, is finding increasing favour. This has resulted in more specific information being acquired as to the reactions of different species to drugs and the dosages required to achieve predictable effects. Reference may be made to two recent articles, by Harthoorn (1963) and Larsen (1963), which refer to the use of tranquillisers, narcotics and muscular relaxants in wild animals. It should be emphasised that, for wild animals, the problem of dosage and administration of a drug or a combination of drugs is very much easier in a zoo than in the wild state. In the latter, the victim seldom stays in the area of capture and the first dose is the only dose administered. This factor necessitates a drug or combination of drugs conforming to the following criteria as outlined by Harthoorn (1963).
1. The margin of tolerance of the mixture used should be wider than the margin of error in estimation of the bodyweights of the animals to be injected.
2. The mixture per unit of bodyweight should be similar for most species. This principle immediately breaks down when muscular relaxants are used.
3. The action of the mixture should be sufficiently rapid for injected animals to be incapacitated before they can make a get-away in thick cover.
4. It should be possible for the animal to recover without assistance.
5. There should be an adequate lower safety margin in relation to the security of the operator.
6. It should be safe to inject the antidote to the immobilising drug even in large quantities.
The volume of the mixture should not be excessive. For practical purposes a 20 ml. projectile syringe is the maximum that can be used for large animals.
With these criteria in mind, it can be appreciated that the veterinarian must have some judgement of the weight of each species and the dose rate of any drug used. A useful reference work in this regard is "Systematic Dictionary of Mammals of the World", by Maurice Burton (1962).
DRUGS USED
TRANQUILLISERS
A range of agents in this group is now available, the earliest used being the phenothiazine derivatives, such as "Largactil" (chlorpromazine) "Sparine" (promazine) and "Trilafon" (perphenazine). More recently ataractic agents, which have a specific action on the anxiety state and less motor and depressive effects, have become available; such drugs include "Librium" (chlordiazepoxide) and "Valine" (Roche).
All these agents fulfil most of the criteria outlined, except that their onset of action is slow, requiring 40 minutes to 1 hour. In a species such as a giraffe, which tends to stay in the area of capture, this is not a real disadvantage but in wild Carnivora, buffalo and rhinoceros, the animal may travel many miles after the injection, or alternatively find cover and await the hunter when he is seeking his prey in the dense undergrowth. Oral administration of tranquillisers in feed or water necessitates a prolonged period of hunger and thirst, due to the highly suspicious nature of most wild animals, especially deer and antelope. Food has to be withheld for at least 48 hours or longer before a wild ruminant will eat medicated feed. In general water restriction is more successful than withholding food. Drugs such as "Librium" and "Valine", however, are soluble only in an oily base which produces a film on the surface of the water, and the animals will not drink. Promazine or chlorpromazine, at a dosage of 1.0 mg per pound in two to four quarts of water, is suitable for larger ruminants such as Wapiti deer, eland and wildebeest, whilst half to one quart is the maximum amount of water antelope and small deer will drink. In Carnivora the drug can be readily incorporated in the required concentration in raw meat.
Tranquillisers are relatively constant in their effect in most species, but require extremely high doses, i.e., 2.5-5.0 mg per pound before safe handling of carnivores can be attempted. For this reason they are seldom used alone, but in mixtures incorporating narcotics or muscular relaxants.
NARCOTICS
The morphine group, or similar preparations such as "Themalon" (Burroughs Wellcome), are mostly used. The advantages of "Themalon" are that it has a suitable antagonist in "Lethidrone" (nalorphine), and that it has fewer side-effects than morphine. If administered on its own, "Thermalon" lacks potency in the wild animal; even 5-6 grams given to a wild ruminant will not prevent it moving. It is particularly valuable when used in combination with hyoscine and phencyclidine, when a fraction of the above dose will bring a large animal down. Like tranquillisers it requires a prolonged period after injection to be effective.
"Lethidrone": This drug is a competitive antagonist to morphine and related compounds such as pethidine and "Themalon". Its most important use is after capture, when "Themalon" or morphine has been used in an immobilising mixture. When the animal is ready to be released an injection of 200-500 mg up to 1.0 g will enable an animal such as a rhinoceros to rise to its feet.
Phencyclidine: ("Sernylan", Parke Davis & Co.) This is a most promising new drug prepared as a stable, white solid, soluble up to 25 per cent in water and ethanol. It produces a cataleptic state in medium-low dosage, followed by a condition resembling anaesthesia at higher dosage rates. When used in conjunction with narcotics and tranquillisers it markedly potentiates their effect. Its rapid action, resembling the muscular relaxants, and its wide margin of safety have led to its incorporation in most immobilising mixtures, Harthoorn (1963). If used alone and in large quantities, it has the disadvantage of a prolonged recovery phase. There are a few reports of its use in different species when used as the sole agent, such as those of:—
(a) Harthoorn (1963)
Cats Low dosage 0.5 mg/lb. (can still
walk).
Medium dosage 1.0 mg/lb. (dogs and cats, prostration).
High dosage 4.0 mg/lb. (prostration, ataxic for three to five days).
Cattle 0.25-0.5 mg/lb. (sternal recumbency).
(b) Rutty and Thurley (1962)
Monkeys 1.0 mg/lb. IV. (docile for handling in ten
minutes).
5.0 mg/lb. IV. (surgical analgesia).
20.0 mg/lb. IV. (clonic spasms).
These authors found the intra-peritoneal route unsatisfactory but, by intramuscular injection, the drug caused sufficient effect for monkey handling in approximately ten minutes.
(c) In an annotation in "Chester Zoo News". November, 1963, it is reported that the drug has been used in bears, monkeys and an elephant at the approximate dose rate of 1.0 mg/lb. bodyweight.
MUSCULAR RELAXANTS
"Flaxedil": This is a relatively short-acting, competitive relaxant but requires large doses to immobilise an animal such as a rhinoceros and, while resuscitation with "Prostigmin" can be effected, paralysis can recur. Harthoorn and Luck (1962) found that the immobilising dose for the elephant could be cut down from 1.2 mg/lb. to 0.9 mg/lb., while 0.8 mg/lb. is enough to halt the animal. When used in combination with hypnotic mixtures it has an added advantage in elephants in that the trunk is immobilised.
"Flaxedil" has been used in the capture of wild ruminants. Atropine is generally administered with the "Flaxedil" and also with the antagonist, "Prostigmin", to eliminate any muscarine-like effects on smooth muscle. In a group of Oribi captured by this method in the Transvaal (Nature Conservation Section, personal communication) the optimum dosage for an animal with an average weight of 40 lb. was 32-35 mg of "Flaxedil" given with 0.25-0.6 mg atropine I/M. "Prostigmin", 1.25 mg. and atropine. 0.5 mg, were injected on capture, recovery occurring within five minutes. At this point 1.0 mg/lb. bodyweight of "Valine" (Roche) was given by intramuscular injection for tranquillisation during transport.
Harthoorn (1962), in a controlled series of observations, found that "Flaxedil" was a safe agent to use to immobilise feral cattle when used with a projectile syringe. The dose of "Flaxedil" varied from 0.5-0.9 mg/lb. bodyweight. Respiratory difficulty was experienced in dosage ranges over 0.7 mg/lb. Atropine sulphate was given at the rate of 5.0 mg per 100 lb. bodyweight if possible five minutes before the muscular relaxant. He found that the antidote, "Prostigmin", should not exceed 1 mg per 100 lb. Larger doses elicited convulsions, and a neuro-muscular blocking action due to "Prostigmin" itself was superimposed on the blocking action of the "Flaxedil".
Succinyl-choline Chloride: This is a rapid, depolarising relaxant. The dose rate is variable but in several wild species the range of dosage is known with some accuracy.
| Bear | 0.33 mg/lb. B.W. I/M | Craighead and Craighead (1960) |
| Monkey | 1.0 mg/lb. B.W. I/M | Thomas (1961) |
| Barbary Ram | 0.1 mg/lb. B.W. I/M | Ibid (1961) |
| Lions | 0.2 mg/lb. B.W. I/M | Ibid (1961) |
| Kob Antelope | 1.7 mg/lb. B.W. I/M | Harthoorn (1963) |
| Wildebeest | 0.025-0.03 mg/lb. B.W. I/M | Harthoorn (1963) |
| Deer* | 0.04 mg/lb. B.W. I/M | Thomas (1961) |
| Deer* | 0.10-0.15 mg/lb. B.W. I/M | Heuschele (1961) |
| Elk | 0.03 mg/lb. B.W. I/M | Thomas (1961) |
| Elephant Seal | 0.91 mg/lb. B.W. I/M | Ling and Nichols (1963) |
| California Sea Lion | 0.1-0.2 mg/lb. BW. I/M | Heuschele (1961) |
* Variations in the dose rate by the two authors is related to the degree of relaxation required. This can range from paralysis of the legs and neck muscles only to complete muscular paralysis. In general the recovery time was longer in Heuschele's series, indicating a higher level of the drug in the body.
These dose rates show marked species variation. Where the species dose rate is not known, the author has found that wild ruminants can be compared with the basic dose for the domestic ruminant, i.e., 0.01 mg/lb. I.V. A factor of four times should be used if I/M administration is desired.
Recovery time is variable but ten to twenty minutes is the normal range in most ruminants. In the elephant seal, Ling and Nichols (1963) found recovery varied from a few seconds to 45 minutes. In wild animals related to the horse and pig, recovery times of two to five minutes can be anticipated.
IMMOBILISING MIXTURES
From what has been stated previously, it is evident that the range of safety and effectiveness of most drugs used alone is very much restricted when compared with the synergistic effects of drugs used in combination. A great advantage of mixtures of narcotic compounds over paralysing drugs is that the dose rate for all ungulates is approximately the same. Also experience in domestic species would indicate that the use of tranquillisers alone for the loading of cattle for transport or slaughter may not always be as effective as previously thought. In the induction of a tranquil state, excitement may occur, Ginsberg et al.. (1963).
Harthoorn (1963) has developed the following mixture for all large ungulates.
TABLE I
| Estimated bodyweight | Phencyclidine | "Largactil" | "Themalon" | "Hyoscine" |
|---|---|---|---|---|
| (lb.) | (mg) | (5% sol. in ml) | (g) | (mg) |
| 1000 | 100 | 5* | 1½ | 50 |
| 1500 | 150 | 7½ | 2½ | 75 |
| 2000 | 200 | 10 | 3 | 100 |
| 2500 | 250 | 12½ | 3¾ | 125 |
| 3000 | 300 | 15 | 4½ | 150 |
* Additional "Largactil" may be injected after capture if necessary.
Method: The "Themalon" is first dissolved in water, then a phencyclidine and hyoscine solution added, (the latter forms a stable mixture), and finally the "Largactil" solution is added.
RESULTS
Rhinoceros
These animals are big, strong and yet very delicate and die easily from bruising or from incapacitating drugs, hence the above mixture may be varied under field conditions. In the White Rhinoceros (Ceratotherium simum), which has a quiet temperament, "Largactil" and "Themalon" together are adequate for most immobilising procedures. The Black Rhinoceros (Diceros bicornis) is an animal of volatile temperament, charges readily and runs with speed and deliberation. In this case the rapid action of phencyclidine is an advantage and the complete mixture (Table 1) is used. Harthoorn (1963) reports 63 successful cases of capture. The author has had opportunity to use it on only one case in captivity. Under zoological conditions we have found that initial narcotisation with chloral hydrate in the drinking water, followed by intravenous thiopentone, is a very satisfactory means of achieving anaesthesia. The method has been described, Larsen (1963), and has since been used on two further cases with similar results.
Giraffe
A relatively quiet animal which stays in the field of capture. Harthoorn (1963) found the following mixture suitable in the greater number of cases.
TABLE II
| Estimated bodyweight | "Largactil" | Morphine | Hyoscine | Time before Immobilisation |
|---|---|---|---|---|
| (lb.) | (mg) | (mg) | (mg) | (minutes) |
| 1200 | 250 | 250 | 50 | 80 |
| 1600 | 375 | 375 | 75 | 90 |
Other Species
Elephants and hippopotamuses react similarly to the rhinoceroses, while buffaloes and wildebeest take a longer time, 30 to 45 minutes, for the mixture in Table I to take effect. Lions can be captured using this mixture with the exclusion of "Themalon".
METHOD OF ADMINISTRATION
The original projectile syringe sold by the Palmer Chemical Company Inc. (Atlanta, Georgia, U.S.A.), using the conventional soda-acid activating mechanism, is still the most commonly used. An explosive cap to activate the syringe is also available, but other than for large animals, such as elephants and hippopotamuses, the explosive force of injection can cause severe trauma. It should be appreciated that the impact of the syringe occurs with considerable momentum and great care must be exercised in shooting at animals less than twenty yards distant. Conversely, 35 to 40 yards is the maximum effective working distance. For distances of less than twenty yards the pistol is better. The unit used at the University Veterinary Hospital cost £A140 in 1963. This cost includes syringes and other accessories. Several modifications of the Palmer "Capchur" rifle have been developed. Other methods of firing a syringe, such as a yew bow, Short (1963), and the cross-bow, have been reported. Their silence in use, and cheapness and simplicity of construction should commend them to anyone working with wild animals.
DISCUSSION
While this paper has described the use of muscular relaxants and the development of mixtures of drugs for the capture of wild animals, the veterinarian in the field who is faced with the handling of cattle under difficult conditions, may well consider the advantages of such mixtures. The use of tranquillisers and narcotic mixtures in the prevention of bruising and loss from transport shrinkage in cattle for slaughter is worthy of more investigation.
References:
- Burton, M. (1962), "Systematic Dictionary of Mammals of the World". (Museum Press: London)
- Craighead, F. and Craighead, J. (1960) — Nat. geogr. Mag., 118: 277
- Ginsberg, A., French, P., McManus, D. and Grieve, J. M. (1963) — Vet. Rec., 75: 996
- Harthoorn, A. M. and Luck, C. P. (1962) — Brit. vet. J., 11:526
- Harthoorn, A. M. (1962) — Vet. Rec., 74: 395
- Harthoorn, A. M. (1963) — Brit. vet. J., 119: 47
- Heuschele, W. P. (1961) — Vet. Med., 56: 348
- Larsen, L. H. (1963) — Aust. vet. J., 39: 73
- Ling, J. K. and Nicholls, D. G. (1963) — Nature, 200: 1021
- Rutty, D. A. and Thurley, D. C. (1962) — Vet. Rec., 74: 883
- Short, R. V. (1963) — Vet. Rec., 75: 883
- Thomas, W. D. (1961) — J. Amer. vet. med. Ass., 138: 263