Antelope Chemical Immobilization and Sedation

Research, zoo applications, conservation and management programs can require the capture and manipulation of antelope. The development of non- and minimally invasive procedures over the years have allowed researchers, veterinarians and management personnel to obtain some data without the need to handle animals. Certain information, however, can only be obtained by capturing animals.¹ Captures are also important for marking individuals in the case of ecological and behavioral studies.

New 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 antelope, 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.

Antelope Biology

Antelope are ruminants belonging to the family Antilocapridae and Bovidae. The pronghorn antelope, Antilocapra americana, is the only member of the former.⁴ Antelope males and the females of some species have unbranched horns attached to the frontal bones of the skull.³ Until the advent of potent opiates, the pronghorn was known to be notoriously difficult to safely capture or anesthetize.⁴

Antelope vary widely in size. For example, the royal antelope weighs an average of about four pounds, whereas the eland weighs up to 1,800 pounds.⁵ Despite being extremely widespread in geography and diverse in size, behavior and habitats, nearly all antelope are large hoofstock, and comparatively large as regards species typically encountered by researchers and wildlife managers in the field. Additionally, all antelope are prey animals, and have evolved with instincts and behaviors gauged to help them survive.

Each species of antelope has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.^3,4 Antelope captures can involve 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. In the case of mortality occurring during capture, this rate is rather easy to measure, while delayed mortality is much more difficult to determine.

The effects of immobilization can considerably differ according to the capture methodology employed. In this regard, the relevant published research agrees that captures by remote delivery of immobilizing drugs via darting lower an antelope’s stress levels, thus decreasing the subsequent capture effects compared to other techniques.³ This is one of the main reasons why chemical immobilization is becoming the preferred capture method, particularly concerning large mammals like antelope.

Drugs Used for Chemical Immobilization of Antelope

There are three basic classes of central nervous system immobilization drugs that are used on antelope:

• Opioids
• Cyclohexamines
• Neuroleptics

Opioids 

• The most potent drugs available for immobilization
• A major advantage is the availability of specific antagonists
• 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
• Common cyclohexamines include Ketamine, tiletamine
• Cyclohexamines should not be used alone and are not reversible
• 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 setting, less stress on antelope is likely to occur than in the field, as zoo animals tend to be far more acclimatized to humans and procedures. In some cases, intramuscular hand injection can be used when working with zoo 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 also widely used in this application; these afford greater distance than approaching an animal for a hand injection without resorting to remote delivery systems. 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 with hand injection, larger bore needles should be used to ensure complete drug delivery.

Remote chemical immobilization is usually carried out by approaching antelope 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. Frightened antelope will have an increased heart rate, higher levels of cortisol and other stress-related biochemicals.² An approach from the ground tends to produce even lower stress levels in antelope, because animals are generally 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.

Analgesia is essential if the antelope’s skin has been breached by anything larger than a hypodermic needle, including biopsy instruments. 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.⁴ These observations can be even more difficult to make in the field than in a clinic or zoo setting, compounding the difficulty in such assessments.

Most of the opioid analgesics (Buprenorphine, Fentanyl, Butorphenol, Oxymorphone, etc.) administered in the early evening, for example, 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.⁵

Reversal Agents for Antelope

Whether general anesthesia or sedation has been used, reversal agents are often required to neutralize sedation or anesthetic agents, thus allowing the antelope 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, 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 anesthesia is being maintained by a gas anesthetic (e.g., isoflurane), 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.⁵

In contrast, injectable anesthetics and sedatives (which may be used for less invasive or higher-risk procedures) do not have this flexibility. Once a dose has been administered, it cannot be “un-administered” to facilitate the end of anesthesia to coincide with the end of the procedure.⁶ 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

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.⁷

Given concerns in the area of conservation and humane treatment, 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.² 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 antelope. One such formulation is the MKBM™ Kit, an original formulation containing:

• Medetomidine hcl 20 mg/ml
• Ketamine hcl 100 mg/ml
• Butorphanol 30 mg/ml
• Midazolam 20mg/ml

The MKBM™ Kit also includes the reversal agents:

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

The MKBM™ Kit was developed for the chemical immobilization of numerous large exotic hoofstock species. It is an excellent choice for anesthetizing antelope, bongo, kudu, gazelle, eland, as well as other African hoofstock and certain domestic wildlife species.

Overall, the drug formulations currently available for immobilizing antelope 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 antelope.

¹Brivio 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.

²Powell RA, Proulx G (2003) Trapping and marking terrestrial mammals for research: integrating ethics, performance criteria, techniques, and common sense. ILAR J 44: 259–276.

³Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed.

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

⁵Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.

⁶Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014.

⁷Plumb’s Veterinary Drugs.

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.

Disclaimer

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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