Deer Chemical Immobilization and Sedation

Research, conservation and wildlife management programs often require the capture and manipulation of deer. The development of less invasive procedures over the years has allowed researchers, veterinarians and management personnel to obtain certain data without the need to handle animals. Some information, however, can only be obtained by capturing animals.¹

Technological advances such as global positioning system (GPS) collars, heat sensitive transmitters and advanced physiological monitoring equipment now allow detailed research on wildlife species such as deer, but still require the initial capture and manipulation of individual animals.² Live captures are also required in conservation biology for animal translocations, reintroductions or population restocking.

Deer Background, Biology and Habitats

Deer are cloven-hoofed ungulates that typically have a compact build, long, slender legs and antlers in the males of the species. The deer family (Cervidae) is very large, and includes most of the species familiar in North America, as well as caribou, elk and moose.³ Cervids are the second most diverse family after bovids (Bovidae, which include antelopes, bison, buffalo, cattle, goats and sheep).⁴ Members of the deer family are found all over the world, except for Australia and Antarctica. Globally, deer habitats encompass wetlands, deciduous forests, grasslands, rain forests, arid scrublands and mountains.

Deer species range from very large to very small. The smallest cervid is the Southern pudu (Pudu puda), which weighs approximately 20 lbs.; the largest is the moose (Alces alces), which can weigh in at 1,800 lbs.^4,5 Except for the Chinese water deer (Hydropotes inermis), all deer species have antlers, and except for caribou (reindeer), only the males of the species have antlers,⁵ which are regrown annually.

Deer are herd animals which are usually led by a dominant male, although in some species the herds are segregated by sex.³ All deer are prey animals, and have evolved with instincts and behaviors gauged to help them survive.

Deer and Chemical Immobilization

Deer captures can involve the risk of mortality, reduction in survival probability or injury of individual animals. Mortality is the most important factor when evaluating the safety level of a capture methodology.^3,4 In the case of mortality occurring during capture, this rate is easy to measure, while delayed mortality is much more difficult to determine.

The effects of chemical immobilization can differ greatly depending upon the capture methodology employed. The relevant published research agrees that captures by remote delivery of immobilizing drugs via darting lower a deer’s stress levels, thus decreasing the subsequent capture effects compared to other techniques.⁶ This is one of the main reasons why chemical immobilization has become the preferred capture method for large mammals like deer.

Drugs Used for the Chemical Immobilization of Deer

There are three classes of central nervous system (CNS) immobilization drugs that are used on deer:

• Opioids
• Cyclohexamines
• Neuroleptics

Opioids

• The most potent drugs available for immobilization
• Specific antagonists readily available
• Reduced volume of drugs are typically required
• The only class of drugs practical for remote immobilization of large animals
• Potentially toxic to humans

Cyclohexamines

• Also known as dissociative agents
• Produce altered consciousness
• Dissociate mental state from environmental stimulation.
• Retain many vital reflexes
• The animal cannot walk but can move tongue, blink, swallow
• The animal may feel some pain
• Should be used in conjunction with other drugs, such as neuroleptics

Neuroleptics

• Also referred to as tranquilizers
• Produce calmness and relaxation
• Do not cause loss of consciousness or alleviate pain perception
• Can cause death before they cause loss of consciousness
• Used in conjunction with other drugs (e.g., cyclohexamines)
• Common neuroleptics include zolazepam, diazepam, xylazine
• Common reversal agents include yohimbine, tolazoline

Chemical Immobilization Techniques for Deer

In a zoo or deer farm, less stress on animals is likely to occur than in the field, as these animals tend to be far more acclimatized to humans and procedures. In some cases, intramuscular hand injection can be used when working with captive animals that are cooperative, or those that have been cornered in squeeze cages or enclosures. When hand injecting, rapid delivery while minimizing risk to the handler or animal is essential. Pole syringes are may be used in these cases, since these afford greater distance than approaching an animal for a hand injection. Drug delivery by pole syringe requires manual injection follow through to administer the drug, as the handle is usually a direct extension of the plunger. As in the case of hand injection, larger bore needles should be used to ensure complete drug delivery.

Remote chemical immobilization is usually carried out by approaching deer and shooting a dart from a helicopter, snowmobile, an off-road vehicle, or from the ground. While this can significantly reduce stress compared to physical capture methods, it still impacts an animal’s stress levels. A frightened deer will have an increased heart rate, as well as higher levels of cortisol and other stress-related biochemicals.^6,7 An approach from the ground tends to produce even lower stress levels in deer, because they will be less frightened than if a noisy vehicle is used. On the other hand, this is more difficult to accomplish, because it requires a closer approach with animals that are extremely alert, fast and agile.

If a deer’s skin has been breached by anything larger than a hypodermic needle (including biopsy instruments), analgesia will be required. Invasive surgeries should be conducted using general anesthetics with the animal at a surgical plane; intraoperative analgesia that continues after anesthetic recovery should be provided in some form to every surgical patient.¹ For analgesic drugs, doses and frequencies of administration are more difficult to gauge, even with close clinical observation for discomfort.⁷ These observations can be even more difficult to make in the field than in a clinic, farm or zoo setting, compounding the difficulty in these assessments.

Most of the opioid analgesics (Buprenorphine, Fentanyl, Butorphenol, Oxymorphone, etc.) will not be effective after 12 hours. Longer‐lasting, non‐steroidal anti‐inflammatory analgesics (NSAIDs) such as Meloxicam, Carprofen, Flunixin, Ketoprofen,etc. have longer durations of action than opioids, and can be administered in conjunction with opioids to increase potency of effect and duration of action.⁷

Reversal Agents for Deer

Whether sedation or general anesthesia has been employed, reversal agents are often required to neutralize sedation or anesthetic agents, allowing the deer to completely recover from being anesthetized. This is even more important in the field than in a clinic or zoo setting, because a chemically-compromised animal will be in danger of injury, predation and other hazards.

Duration of anesthesia is influenced by the drugs used, species or subspecies, age, sex, body weight, procedure performed and the amount of stimulus during the procedure. Due to all the factors that influence duration of anesthesia, the literature maintains that anesthetic drugs should always be titrated to effect. If gas anesthesia (e.g., isoflurane) is being used, titration of anesthetic depth can be controlled almost immediately by adjusting the amount of anesthetic gas being administered to the animal. In addition, anesthetic duration can be extended for as long as the anesthetic gas is administered.⁶

Injectable anesthetics and sedatives (which may be used for less invasive or higher-risk procedures) however, do not have this flexibility. Once a dose has been administered, it cannot be “un-administered” to facilitate the end of anesthesia coinciding with the end of the procedure.⁸ Here, reversal drugs are used to bring about the desired effect.

Atipamezole is a synthetic α2-adrenergic antagonist. Developed to reverse the actions of compounds such as medetomidine and dexmedetomidine.

Naltrexone hydrochloride is an opioid receptor antagonist that is used in veterinary medicine to block receptors as a reversal agent for opiate agonists such as butorphanol.

In recent years, great care has been taken with chemical immobilization protocols and drug development to keep these within safety margins through the use of novel anesthetics, including combinations of true anesthetics, neuromuscular blockers and tranquilizers.⁶ Thus, modern chemical immobilization techniques have dramatically reduced the side-effects of drugs and mortalities. Additionally, the use of antagonists to anesthetics is now widely employed, as this avoids the undesirable and potentially harmful effects of drugs and facilitates speedy recovery from chemical immobilization events.^1,2

In recent years, veterinary custom compounding pharmacies have widely expanded the variety, availability and efficacy of immobilizing drugs through the development of custom formulations for wildlife such as deer.

One such formulation is the MKB2™ Kit, an original formulation containing:

• Medetomidine 20 mg/ml
• Ketamine 100 mg/ml /
• Butorphanol 50 mg/ml

The MKB2™ Kit also includes the reversal agents:

• Atipamezole 40mg/ml
• Naltrexone 50 mg/ml

The MKB2™ Kit was developed for the chemical immobilization of numerous large exotic hoofstock species. It is an excellent choice for anesthetizing elk, deer, fallow deer, white-tailed deer, roe deer and certain exotic wildlife species.

Overall, the drug formulations currently available for immobilizing deer and other large wildlife species have been refined to a degree that eliminates much of the risk that existed just a few years ago. With the right drug formulations, proper planning and safety precautions in place, experienced personnel can have the expectation of effective and incident-free chemical immobilization of deer.