Chemical Restraint of Zoo Animals
Wild and exotic animals are far more susceptible to stress and injury during capture, handling and restraint than domestic species, even in a zoo setting, wherein they have often been largely acclimatized to captivity. Even relatively minor procedures such as blood collections and clinical examinations can be sufficiently distressing to a wild animal as to significantly jeopardize its health.1 Additionally, many wildlife species can be potentially dangerous to human handlers, so human safety must also be taken into consideration. Therefore, a chief objective of every capture and restraint procedure performed in the zoo setting must be to minimize the stress on the animal whilst maximizing the safety of human handlers.
The restraint and handling of zoo animals typically requires chemical immobilization and anesthesia. The degree and type of sedation will generally vary depending upon the type of procedure(s) being performed. Advance planning for chemical immobilization events should always include:
- A thorough knowledge of the species to be handled, including its behavior, reaction to stress and the appropriate physical and chemical restraint procedures
- A full consideration of why the animal needs to be handled, including exactly what procedures are to be performed, as well as their nature
- The equipment and facilities required
- The restraint procedures to be employed
- The best time to undertake the procedure
- Recovery conditions
Principles of Anesthesia for Zoo Animals
The basic medical principles of exotic and domestic animal anesthesia are essentially the same. The selection of appropriate drugs, drug dosages, drug delivery, appropriate conditions for delivery, and the legal issues surrounding the chemical restraint of free-ranging wildlife often differ, however. With the advancement of chemical immobilization procedures in recent years, the chemical restraint of zoo and wildlife species has improved significantly, with safer and more efficient drugs, portable monitoring equipment, and precise methods of drug delivery.
Modern immobilizing techniques are more humane methods for the handling of wild animals, and this has drastically reduced the side effects of drugs and mortality. Further, the use of antagonist/antidotes for anesthetic agents is being more widely utilized to avoid the undesirable effects of drugs and for speedy recovery of wildlife species. Thus, chemical restraint has been successfully employed by the wildlife veterinarians to relocate or treat animals in the captivity as well as in the wild, resulting in the rescue of many rare and endangered species. These advanced procedures have become increasingly popular and are being adopted by zoos for the safer handling of wild animals. However, the modern capture methods require a high degree of expertise and experience, as well as basic knowledge of anatomy, physiology and the behavior of the animal(s) to be captured.
Many different classes of compounds, including anesthetics, analgesics, sedatives and tranquilizers have been used to immobilize wild animals. Only a few of these compounds can be used on a regular basis within the U.S. however, due to federal regulations. One of these regulations, the FDA's Controlled Substances Act of 1970, restricts the use and distribution of some of the more potent drugs, such as opioids.3 Fortunately, there are other drugs which are just as effective, safer and more accessible.
Typically, a zoo’s on-staff or consulting veterinarian will select the best drug or drug formulation for each situation according to the physiology and behavior of the animal, as well as the practitioner’s experience and professional preference. Procedures chosen by the veterinarian for zoo animals in a controlled environment logically differs from procedures chosen for free-ranging animals.
Drug Delivery Methods for Zoo Animals
Oral Dosing
Oral delivery of immobilizing agents is rare with free-ranging wildlife, but can be more successfully carried out in a zoo setting. In such cases for example, an animal may be given an oral sedative in its food or water prior to more heavy sedation and anesthesia being administered once the animal is calmed. Oral delivery of certain tranquilizers in bait has also been known to improve the darting success of some large carnivores.1
Injection by Hand
Intramuscular hand injection can sometimes be used when working with smaller, cooperative mammalian species. When hand injecting, rapid delivery while minimizing risk to the handler and animal is very important. To speed drug delivery, a needle bore larger than might be selected for hand injection under a more controlled circumstance will be necessary. The use of syringes that require needles to be twisted on will help prevent needles from coming off the syringe during injection will increase safety.2
Pole Syringes
Drug delivery by pole syringe requires manual injection facilitate IM injection at a safer distance. The exception to this is the use of commercial spring loaded or air pressurized pole syringes. As with hand injections, larger bore needles are needed to ensure complete drug delivery.
Darts
Projectile syringes or darts are an extremely useful means of injecting drugs intramuscularly (i/m) in zoo animals. They can be used on a wide range of species, from small carnivores and primates to the largest of ungulates. Remote delivery of anesthetics to zoo animals is most often accomplished using a variety of syringe darts that are propelled by blow pipes or specialized dart guns. Dart guns range from very heavy duty rifles that use a .22-caliber system, to very lightweight pistols that powered by air or CO2. Dart types range from lightweight air-pressured systems to charge-powered injection systems.3 Dart impact is a product of the mass of the dart times the square of the terminal velocity the dart is traveling at the time of impact. The lightest dart possible for a specific operation and the lowest velocity possible to accurately and precisely hit a target should be used.2
Drug potency is key when remotely delivering anesthetics to zoo animals. The goal is to immobilize the animal with one dart. Most drug combinations should fit into a 2-, 3-, or 4-mL dart.1 Additionally, more concentrated anesthetics will result in less tissue trauma due to decreased volume injected and will be absorbed faster, ultimately resulting in a quicker induction. Custom formulations acquired from veterinary compounding pharmacies are ideal for such applications. Another consideration in drug selection for the immobilization of zoo animals is a drug’s ability to be antagonized. Depending on the environmental conditions and target animal, rapid recovery at the desired time can be a huge advantage when immobilizing wildlife. The proper reversal agents for anesthetic agents can also be obtained through veterinary compounding pharmacies, often in kit form in the appropriate concentrations.
Inhalant Anesthesia
Inhalant anesthetics such as halothane and isoflurane are usually used for general anesthesia in surgical procedures once an animal has been heavily sedated with other drugs using the above means. Halothane is a halogenated alkane that can be used successfully with the majority of wild animal species. It is compatible with all commonly used injectables, which are usually used as inducing agents. However, halothane sensitizes the myocardium to catecholamines and can induce arrhythmias; it can also induce lung and liver damage due to toxic metabolites. Isoflurane is a halogenated ether that can be used in lieu of halothane. It is metabolically stable and thus induces far less organ toxicity and myocardial sensitization, while still providing rapid induction, recovery, depth regulation, good muscle relaxation and analgesia.4
Interested in learning more about safe capture? The San Diego Zoo now offers courses in safe capture techniques and best practices. Learn reliable, safe, and effective techniques for the species you work with and the scenarios you encounter!
2Nielsen, L. Chemical Immobilization of Wild and Exotic Animals. (1999) Ames, Iowa, Iowa State University Press.
3Kreeger TJ, Arnemo JM. Handbook of Wildlife Chemical Immobilization, 3rd ed. Sunquest Publishing, 2007, 432 pages.
4Bush, M. (1992). Remote drug delivery systems. Journal of Zoo and Wildlife Medicine, 23 (2): 159-180.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
Our pharmacists are also encouraged to develop strong working relationships with our veterinarians in order to better care for veterinary patients. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.
Disclaimer
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