Axis Deer Chemical Immobilization and Sedation

Research, conservation and wildlife management programs often require the capture and manipulation of wild hoofstock. Over the years, the development of less invasive procedures has allowed researchers, veterinarians and management personnel to obtain a great deal of data without the need to physically handle animals. Some information, however, can only be obtained by capturing animals.¹

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

Axis Deer Background, Biology and Habitats

Deer are cloven-hoofed ungulates that 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 The Axis deer (Axis axis) is a deer species that is native to the Indian subcontinent, although they have been introduced into approximately one dozen other countries, including the United States and some European nations.

The Axis deer is a visually striking animal with an orange-brown coat, spotted body and short tail.⁴ They have faint stripes that are paler in color around the eyes. Males have black spots on their faces and three tines on each of their three-foot antlers. Both males and females have white markings which run in rows along the length of their bodies. They also have a dark stripe running along the length of their backs which are bordered by a row of spots.⁵

The Axis deer’s highest period of activity is in the morning and late afternoon.⁶ During the day, they can usually be found resting in the shadows. They tend to remain near areas where water is plentiful, where they can be found drinking in the mornings and evenings. Axis deer are always on the alert, in anticipation of a sudden appearance of a predator. They are vocal animals that will bellow or bark when alarmed.

Axis deer are herbivores, with a diet consisting of grasses, flowers, and fruit that has fallen from trees. In their native range during the monsoon, grasses and sedges become the main source of food for these animals.^5,6 They will also eat mushrooms that are rich in proteins and nutrients.⁴

Axis deer are sociable animals, with herds comprised of from 6–30 individuals. Most larger herds will have two or three stags. Males live in a hierarchical system with larger and older males dominating smaller and younger ones.⁵ Mature females and their fawns typically form matriarchal herds. Axis deer are polygynous, meaning that a male will mate with multiple females. During mating season, males will start bellowing, which signals the beginning of breeding, which takes place in April or May. The Axis deer’s gestation period lasts 210–225 days. They produce young every year, with females giving birth to 1 or 2 fawns at once.⁴

Axis Deer and Chemical Immobilization Risks

The capture of Axis deer 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.^7,8 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.⁷ 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 Axis Deer

There are three classes of central nervous system (CNS) immobilizing drugs that are used on Axis 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

In a zoo or on a deer farm, less stress on animals is likely to occur than in the field, since animals in these facilities will be far more acclimatized to humans and routine 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 is essential, as this will minimize risks to the handler and animal. Pole syringes may be used in these cases, since these afford greater distance than approaching an animal for a hand injection.

Remote chemical immobilization is usually carried out by approaching Axis 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 does impact 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.^8.9 An approach from the ground tends to produce even lower stress levels 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 an Axis 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.⁸

Most of the opioid analgesics (e.g., Buprenorphine, Fentanyl, Butorphenol, Oxymorphone) are not effective after 12 hours. Therefore, it is recommended that longer‐lasting, non‐steroidal anti‐inflammatory analgesics (NSAIDs) such as Meloxicam, Carprofen, Flunixin, Ketoprofen be used, since these 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 (Antagonists)

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

The drugs used, species or subspecies, age, sex, body weight, procedure performed and the amount of stimulus during the procedure all have an effect on the duration of sedation/anesthesia. Due to all the factors that influence duration of sedation/anesthesia, the literature maintains that immobilizing 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.⁹

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, atipamezole safely and reliably reverses the effects of these compounds and is widely used in small and large animal practices, as well as in wildlife applications.⁹

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. It is also used for the treatment of recurring, compulsive animal behavior disorders such as tail-chasing and self-mutilation such as acral lick dermatitis. The time from administration to Naltrexone taking full effect is reported to be between 1 to 2 hours. The effects of this medication are short-lived, meaning they will stop working within 24 hours, although the benefits may be prolonged if an animal has decreased kidney and/or liver function.⁹

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.⁸ 

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 other exotic wildlife species.

Today, the drug formulations currently available for immobilizing Axis 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 Axis deer.