Why Do We Capture Animals?
Unlike earlier times in human history, the need for capturing wild animals today extends far beyond the need for clothing and food. Today, the capture of wild species for research and conservation projects is a concern that is widely shared globally.1 A wide array of research, conservation and animal management programs focusing on wildlife requires the capture and handling of wild animals.
While the development of noninvasive and minimally invasive procedures has allowed biologists and wildlife managers to obtain much information without the need to handle animals, specific data can often be collected only by capturing animals.1 Capture is also important for marking individuals for ecological, behavioral and breeding studies. New technological advances such as global positioning system (GPS) collars and advanced physiological monitoring equipment allow detailed and innovative research on wildlife, but require the initial capture and manipulation of the animals.
Reasons for Wild Animal Capture
Today, wildlife species are captured for the purposes mentioned above, as well as for the stocking of zoos, aquaria (e.g., marine mammals in water parks), theme parks and for the maintenance of wildlife and game reserves. In captive breeding programs, wild animals are often bred in captivity in order to maintain the viability of certain protected or endangered species. In such cases, the initial breeding stock must naturally be captured in their natural habitats. Live captures are also required in conservation biology for animal translocations and sometimes are an alternative to lethal control in management situations in which human safety and properties may be at risk.1
While the reasons to perform capture of wild animals remain clear, efforts are also made by governing bodies and amongst those engaged in animal capture to ensure ethical standards and the validity of research results. This is because the effects of capture can carry direct risks such as the death of or injury to an animal, and different capture methodologies pose different risks. Thus, mortality rates are the most important criteria for the evaluation of the safety levels of capture methodologies.2
Methods of Wild Animal Capture
The effects of animal capture can differ considerably based upon the capture methodology involved. There are two basic methods of animal capture, these being physical immobilization and chemical immobilization. The former is achieved through the use of a wide range of restraint devices (traps, snares, nets and the like), while the latter is achieved through the use of immobilizing drugs (sedatives and anesthetics).
Studies have assessed the effects of capture on a number of behavioral metrics in free-ranging wildlife. The impacts of different methodologies have included include displacement from the areas surrounding capture sites, altered habitat use, depressed movements and reductions in activity patterns.1,3 The relevant published research indicates that captures by remote delivery of immobilizing drugs by darting lowers an animal’s stress levels and decreases the subsequent capture effects as compared to other techniques.1 It is for this reason that chemical immobilization has become prevalent in the capture of large mammals.
However, the drawbacks of chemical immobilization include drug-induced side effects depending on the specific drug(s) used, the stress caused during the approach, and the stress caused by the animal’s displacement, which is often necessary in order to perform various procedures. Immobilizing drugs are never completely devoid of toxicity and the induction of sedation invariably carries the risk of severe side effects.1 Through the improvement of capture protocols and drug protocols and formulations however, veterinarians, researchers and wildlife managers have been able to reduce the mortality rate of this methodology to minimal levels.3
The type of anesthesia administered to wildlife depends on a number of factors, including the species, type of procedure, need for the procedure, the animal’s age, sex and medical history. Occasionally, the veterinarian, wildlife manager or biologist will determine that more than one type of anesthesia will be appropriate for a certain procedure.
Sedatives allow an animal to relax and become far less responsive to moderate discomfort. Sedatives are often given for carrying out diagnostic procedures that are not especially painful but which might be uncomfortable. They are also used in drug formulations (combinations) and as preanesthetic agents prior to general anesthesia.
General anesthesia places the entire body, including the brain, into a state of unconsciousness, during which the animal has no awareness and feels nothing. General anesthesia is administered by injection or through a breathing mask, or sometimes via both routes. In order to control the animal’s breathing during a surgical procedure, the animal may be intubated, which involves the insertion of a flexible tube down the windpipe.
Drug Classes Used in Wildlife Applications
Sedatives and Tranquilizers – Although the terms “tranquilizer” and “sedative” are often used interchangeably, these drugs belong to two different classes. Tranquilizers include such drugs as acepromazine, diazepam and midazolam, while sedatives include drugs like medetomidine. Tranquilization and sedation are dose-dependent effects of the drugs in both classes.4
Opioids – There are two classes of opioids: pure mu-agonists such as morphine, oxymorphone, hydromorphone, fentanyl and meperidine, and partial mu-agonists such as buprenorphine. The combination of an opioids and tranquilizers provides more sedation and analgesia than either drug would if used alone.
Anesthetics – (dissociatives) Ketamine, propofol, and thiopental are anesthetic drugs that are most widely used in veterinary medicine. Administration, signs and stages of anesthesia are often the same for commonly used dissociative anesthetics.
Alpha-adrenergic agonists (α– adrenergic agonists) – These are a class of sympathomimetic agents that selectively stimulates alpha adrenergic receptors.4 Drugs such as xylazine, romifidine, detomidine, and medetomidine are members of this class and are used frequently in veterinary medicine.
Inhalant anesthetics – Inhalants such as sevoflurane and isoflurane are nonflammable, nonexplosive, volatile liquids that are widely used in veterinary practices. They are only occasionally used with wild animals however, since they must be used with of precision vaporizers which can be impractical under field conditions.
Drug formulations – It has long been known that formulations of different drug classes can have synergistic effects, as well as facilitating smaller doses of drugs that produce undesirable side effects. For example, the combination of xylazine and ketamine has been used for many years in veterinary practices. This has allowed veterinarians to reduce drug dosages and enhance muscle relaxation and duration of effect in their patients; this combination has also been associated with faster and smoother induction.3
Custom formulations acquired from veterinary compounding pharmacies have proven to be ideal for wildlife applications. Depending on the environmental conditions and target animal, they can provide rapid, smooth and safe induction, which is a huge advantage when immobilizing wildlife. The proper antagonists for anesthetic agents can also be obtained through veterinary compounding pharmacies, in kit form in the appropriate concentrations.
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!
1Brivio, F., et al. Assessing the Impact of Capture on Wild Animals: The Case Study of Chemical Immobilisation on Alpine Ibex. PloS one vol. 10,6 e0130957. 25 Jun. 2015.
2Arnemo, J. et. al. (2006) Risk of capture-related mortality in large free-ranging mammals: experiences from Scandinavia. Wildl Biol 12: 109–113.
3Arnemo, J., Kreeger, T. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing.
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.
The information contained in this blog post is general in nature and is intended for use as an informational aid. It does not cover all possible uses, actions, precautions, side effects, or interactions of the medications shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular medication. You should consult your veterinarian about diagnosis and treatment of any health problems. Information and statements have not been evaluated by the Food and Drug Administration ("FDA"), nor has the FDA approved the medications to diagnose, cure or prevent disease. Medications compounded by NexGen Pharmaceuticals are prepared at the direction of a veterinarian. NexGen Pharmaceuticals compounded veterinary preparations are not intended for use in food and food-producing animals.
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