Chemical Immobilization of Wild and Exotic Animals
In recent decades, conservation efforts and the endangered status of certain wildlife species have become more prominent among wildlife biologists and lay persons alike. Innumerable conservation efforts focused on wild animals (including mammals and their ecosystems) are currently being carried out. These conservation and management programs often rely on research methodologies that require the handling of animals. The related purposes range from radio-collaring, procurement of biomedical samples for research purposes to the translocation of the animals to another area. Restraining wild animals is often required in case of most procedures. This can be for routine health checkups, research purposes or for conservation and management purposes. The capture and handling of zoo animals also plays an important role in wildlife conservation and management.
Although physical restraint is usually a straightforward process, this can pose risk and undue stress to animals, and it has several limitations. With some large species, physical restraint is often either impractical or unachievable. Thus, chemical restraint is one of the most reliable alternatives for restraining wildlife species, and it has become a valuable tool in wildlife conservation research and management.
Principles of Wildlife Anesthesia
The basic medical principles of wildlife anesthesia 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.
Drug Delivery Methods
Oral Dosing
Oral delivery of immobilizing agents is rare with free-ranging wildlife, but some specific applications do exist. Oral delivery of certain tranquilizers in bait has been known to improve the darting success of some large carnivores, for example. Some success has been reported with giving primates heavy tranquilizers orally in food items as well, but it is rare to be able to repeat this procedure once animals have experienced it.1 When using oral delivery in the field, it can be difficult to target specific animals, as animals of different sizes or different species can accidentally take the bait.
Injection by Hand
Intramuscular hand injection can be used when working with smaller mammalian species that have been trapped in box traps or leg-hold traps, or with ungulates that have been captured in nets. 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.
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
Remote delivery of anesthetics to wildlife is most often accomplished using a variety of syringe darts that are propelled by blow pipes or a variety of dart guns. Unlike oral dosing, they permit targeting of specific animals and allow the delivery of anesthetics from a greater distance. These can present problems when working with smaller animals, since most delivery systems are not very accurate. Further, the ideal target areas are limited even on large animals. 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. The force at which the dart impacts a target is a critical consideration when remotely delivering anesthetics.2 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. The literature suggests never using a charge-powered system on animals weighing less than 15 kg, but rather using lightweight non-explosive darts with a controlled air or CO2 powered delivery system.
Drugs for Chemical Immobilization
There are numerous peer-reviewed and published sources available for veterinarians and wildlife managers. Since not all findings are published in peer-reviewed literature and because of the long time-lag between discovery and publication, consulting with wildlife veterinarians who routinely immobilize the target species is prudent. Ideally, the chosen drug or formulation should have a high therapeutic index.1,2 The average size of the species being immobilized might be known, but the weight of an animal in the field is generally impossible to determine. Since the goal will be to rapidly move animals into the Stage III level of anesthesia, underdosing an animal can leave them in Stage II anesthesia, where they are conscious and hyper-excited, increasing their susceptibility to hyperthermia, trauma and capture myopathy.3
Drug potency is key when remotely delivering anesthetics. 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 wildlife immobilization is the 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.
Drug Dosages and Conditions
Just as with drug selection, drug dosages can be found in published literature but it consulting with a veterinarian who has experience immobilizing the target animal is advised. Rarely will a team in the field know the exact weight of the wild animal being immobilized, but most anesthetic agents used for capturing wildlife have high therapeutic indexes, so a good weight estimate will be needed. Stress, hyperthermia and capture myopathy are important concerns when capturing wildlife as well, and capture operations should be designed to minimize these dangers.1-3 In addition to drug selection and delivery, a successful immobilization will require that factors such as the animal’s physical and psychological condition, age, ambient temperature, season, and time of capture are considered.
Anyone involved in the chemical immobilization of wildlife should be aware that all of the drugs used for wildlife chemical immobilization are prescription drugs and require use by or under order of a licensed veterinarian. Further, many of the anesthetic agents used for wildlife immobilization are controlled substances and require licensing by the Drug Enforcement Administration (DEA) in the United States.
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.
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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