Eld’s Deer Chemical Immobilization and Sedation

The Eld's deer (Rucervus eldii) is indigenous to Southeast Asia. These are large deer that are considered magestic in appearance. Their legs are long and thin, and they have slender bodies with a large head and ears. Their rough coats change color with the season. In summer, they are reddish-brown, and dark brown in winter. Stags often have darker coloring than hinds (females) and have a thick mane of long hair around the neck.¹

Eld’s deer stags have large lyre-shaped antlers; these sweep back in a curve of about 40 inches in length, with one smaller tine growing toward the front of the head. Antlers are shed every year and reach their largest size during the breeding season.^2,3 Male Eld’s deer grow to about 71 inches in length and weigh from 276 to 386 pounds. They are taller and larger than the hinds, which stand about 60 inches tall.

In their native ranges, Eld’s deer inhabit suitable forest habitats, lowland valleys and plains, avoiding dense forests and coastal areas. This also includes monsoonal forests. Today, they occur in a number of protected areas throughout these areas and have been introduced to numerous countries as game animals, including the United States.³

Rucervus eldii are primarily nocturnal deer. Throughout most of the year, stags tend to be loners, except in the spring when mating commences. Females are generally found alone or in pairs with their young. They remain in close association with their fawns and other female-fawn pairs. Larger groups are often formed when males join groups of females prior to the breeding season, and groups of up to 20 animals are common.²

Eld’s Deer and Chemical Immobilization

Research, conservation and wildlife management programs often require the capture and manipulation of Eld’s deer. Over the years, the development of less invasive procedures 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.⁴

Global positioning system (GPS) collars, heat sensitive transmitters and advanced physiological monitoring equipment now allow detailed research on wildlife species such as Eld’s deer, but still require the initial capture and manipulation of individual animals.⁵ Live captures are also required in conservation biology for animal translocations, reintroductions or population restocking.

Capturing Eld’s 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.^5,6 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 such as Eld’s deer.

Drugs Used for the Chemical Immobilization of Eld’s Deer

There are three classes of central nervous system (CNS) immobilization drugs that are used on Eld’s 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 Eld’s Deer

In a zoo or on a 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 animal 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 Eld’s 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.⁴ 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 Immobilized Eld’s 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, 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.^7,8

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.⁸

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 Eld’s 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 Eld’s deer.

¹animaldiversity.org.
²nationalzoo.si.edu.
³animalia.bio.
⁴Brivio F, Grignolio S, Sica N, Cerise S, Bassano B (2015) Assessing the Impact of Capture on Wild Animals: The Case Study of Chemical Immobilisation on Alpine Ibex. PLoS ONE 10(6): e0130957.
⁵Powell RA, Proulx G (2003) Trapping and marking terrestrial mammals for research: integrating ethics, performance criteria, techniques, and common sense. ILAR J 44: 259–276.
⁶Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed.
⁷Nielsen, L. Chemical Immobilization of Wild and Exotic Animals. (1999) Ames, Iowa, Iowa State University Press.
⁸Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.