Chemical Immobilization for Black Bear

Immobilization is the imposed restriction of movement of all or part of an animal’s body, either by physical or chemical means. Typically, immobilization is used to facilitate management of some form (e.g., health, safety, conservation), and it is a common practice in many animal management scenarios. Physical immobilization usually involves traps (e.g., pitfall, cage, leg-hold or box traps; snares, crush cages, plastic tubes or restraint boards), or direct handling restraint. Chemical immobilization is achieved using drugs which have a range of effects, from sedatives which produce a systemic muscular paralysis to anesthetics which produce unconsciousness.

Wildlife researchers often need to immobilize wild animals to mark them for identification, to provide veterinary treatment or to relocate them for reasons of human or animal safety. Typically, marking for identification involves ear notching, digit or tooth removal, tagging and banding or the attachment of radio-transmitters.

While physical immobilization is often impractical when capturing larger and potentially dangerous animals such as bears, in the case of chemical immobilization, there are different cautionary issues. Immobilizing drugs have the potential to disturb normal regulatory systems, particularly respiratory and thermo-regulation, which in turn can lead to negative outcomes such as respiratory depression, over-heating (hyperthermia), lowered blood pH (acidosis) and oxygen deficit (hypoxemia).¹ These can give rise to neurological or myocardial problems, as well as carrying the potential for multi-organ failure. Being chased for an extended period of time by ground or air for the purposes of darting can lead to intense muscular strain and hyperthermia. This can lead to capture myopathy syndrome, which can lead to death from minutes to weeks after the capture event.³

Immobilizing drugs also have the potential to perform differently in combination, as well as in individual animals, depending on their age, sex, health, etc. Dosages often have to be estimated for animals of unknown weight, potentially complicating capture protocols. While these scenarios would be unthinkable in human medicine, they are often routine in situations where wild animals need to be immobilized.

The Need for Safe & Effective Immobilization

The immobilization of large wild animals such as bears poses significant challenges and risks for target animals and the humans involved in immobilizing them. Drug choices and combinations must be of proven safety for the target species and calculated for the weight, age, physiological and reproductive status, body-condition and presence of young or companions. If the induction of anesthesia is too slow, it can increase the risk of physical injury to the animal (e.g., lacerations, limb injuries, head trauma).^1,3

The black bear (Ursus americanus) is the smallest of the North American bears. It is a large, stocky animal, about five feet in length and standing about three feet at the shoulder. Males typically weigh between 200 to 500 pounds (lbs) and females weigh between 100 to 300 lbs. A black bear’s size and weight depends upon the type and abundance of food it eats, its social status, and the time of year. Some bears captured in the fall season have weighed more than 800 lbs.²

In the wild, it is frequently necessary for wildlife managers to capture black bears in their natural habitats, but it is also quite common that a bear will need to be moved out of a conflict situation due to its encroachment on human populations.

Black bear damages to personal property are difficult to calculate. In a 1998 report, bear damaged more than $650,000 of visitor property in Yosemite National Park. This figure is likely greater than that of other locations of equal size, however, due to the concentrations of reliably available foods and the abilities of bear to learn how to obtain them.² Among the most expensive damages to property is forced entry into motor vehicles and collisions on roadways. While most collisions only involve vehicle damage, bodily injury can also occur.

“The black bear is a challenging species for wildlife agencies to manage due to its size, intelligence, extensive range, food habits, and adaptability, as well as societal views. In North America alone, agencies receive more than 40,000 complaints about black bear annually. Black bears are known as ‘food-driven’ animals, meaning most conflicts result from a bear’s drive to meet its nutritional needs. Not surprisingly, an overwhelming proportion of conflicts are related to their use of anthropogenic (human) food sources, such as garbage, bird food, and crops.” (usda.gov)

Considering the above, chemical immobilization is typically used to temporarily immobilize black bears. It is most frequently administered via a dart fired from a capture gun, or via a two meter-long jab-stick with a syringe mounted on the end.¹

In order to reduce the likelihood of injury to the target animal, remote drug delivery systems should (Cattet et. al., 2005):

• Hit the target animal with high accuracy
• Employ lightweight, slow-injection, low-velocity (40-50 m/s) darts
• Use side-ported needles and large diameter needle seals

In some cases, blow pipes may be used to administer immobilizing drugs. This tends to result in fewer injuries, since blow pipes are powered by the lungs of the operator, with the drug(s) being injected via low air pressure. Syringes and needles may be used if the bear is already immobilized and an additional dose is required.

Advantages of remote drug delivery when capturing/immobilizing black bears include:

• The method can be used under a variety of circumstances
• Capture guns are generally effective at long range
• Remote drug delivery offers an alternative to destruction when removal is necessary
• The method is relatively inexpensive

Disadvantages of remote drug delivery when capturing/immobilizing black bears include:

• Slow induction—Drugs can take considerable time to take effect, during which time the bear may flee, climb a tree, enter water or become aggressive.
• There is a potential for overdosing if more than one dart is required
• Close range delivery can result in injury or death, particularly if vital areas are hit (a treed bear, for example, can be very difficult to dart with accuracy)
• Immobilizing drugs can be potentially dangerous to personnel in the field

Drugs for the Chemical Immobilization of Black Bear

Immobilization by the administration of one or more drugs to capture a free-ranging bear by remote drug delivery or to facilitate the safe handling of a bear that has been captured by other means has become a common practice in North America.¹

The method of remote drug delivery should be selected for its effectiveness under the intended capture scenario, and for its safety to the user and target animal. Blowpipes or pistols (CO₂- or air-powered) may be used to deliver small volumes of drug to bears over short distances under the right conditions. For drug volumes greater than 3 mL or over distances greater than15 m, CO₂-powered rifles or powder-charged rifles with power adjustment capability should be used.³

According to wildlife management literature published by the United States Department of Agriculture (USDA), “the safest, most commonly used pharmaceuticals for immobilization are Telazol (tiletamine and zolazepam), a combination of Ketamine/Xylazine, or ‘BAM’ (butorphanol/azaperone/medetomidine).” Chemical Immobilization of Wild and Exotic Animals (Nielsen, 1999) recommends the ketamine/xylazine combination for black bear, as well as etorphine/carfentanil combinations.⁴

Mentioned above, the “BAM” formulation is frequently used for bear and other species of wildlife, as it provides a low-volume, reversible alternative to other immobilizing drug combinations. Butorphanol is a synthetically derived opioid agonist-antagonist analgesic of the phenanthrene series, with a potency of about four to seven times that of morphine. Azaperone is a butyrophenone tranquilizer that causes tranquilization and sedation, antiemetic activity, reduced motor activity, and inhibition of CNS catecholamines. Medetomidine has been shown to be useful for anesthesia and immobilization in zoo animals. An α-2-adrenoreceptor agonist with sedative and analgesic properties, medetomidine is widely used by veterinarians as both a surgical anesthetic and analgesic in wild and exotic animals.

¹Wolfe, Lisa & Johnson, Heather & Fisher, Mark & Lance, William & Smith, David & Miller, Michael. (2016). Chemical immobilization in American black bears using a combination of nalbuphine, medetomidine, and azaperone. Ursus. 27. 1-4. 10.2192/URSUS-D-15-00018.1.

²usda.gov.

³Cattet, M. et. al. An Evaluation of Long-Term Capture Effects in Ursids: Implications for Wildlife Welfare and Research, Journal of Mammalogy, Volume 89, Issue 4, 15 August 2008, Pages 973–990.

⁴Nielsen, L. Chemical Immobilization of Wild and Exotic Animals. Ames : Iowa State University Press, 1999.

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.

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