Impala Chemical Immobilization and Sedation

Known for their iconic appearance and spectacular leaps, the impala (Aepyceros melampus) is a widely-distributed African ungulate comprised of several subspecies. Impala are most often found in Kenya, Zimbabwe, Uganda, Zambia, Botswana, and Southern Angola to northern South Africa, and are one of the most dominant species of antelope on the African savannah. The most common subspecies in East Africa is Aepyceros melampus rendilis; Aepyceros melampus petersi, the black-faced impala, is distributed further south. There are other proposed subspecies (up to 4 additional) that are less well known; controversy as to their designation is ongoing.¹

Impala are light to reddish-brown in color with white undersides and a black stripe that extends from the top of the rump down the back of each thigh.² The rams have lyre-shaped horns that reach a length of around 30 inches. The impala stands 30 to 36 inches high and weighs 90 to 170 pounds. Impala males are approximately 20% heavier than females.

Impala are both diurnal and nocturnal, being most active immediately after sunrise and just before sunset. Female impalas and their offspring gather into herds which number from 15 to 100 individuals. The home range of a herd covers a territory that varies from 80 to 180 hectares.³ During the wet season, females become highly territorial and defend the home ranges. Young males form non-territorial bachelor herds of up to 30 individuals. During the dry season, male and female herds mix together.

Impalas take part in a polygynous mating system where each male mates with numerous females.³ From March through May, pregnant females live in isolation to give birth. Their gestation period lasts from 195 to 200 days, after which females give birth to a single calf. The mother and calf then rejoin the herd.²

Impala are able to adapt to different environments of the savannas. In some areas, they are grazers and browsers in others. Impala herds typically stay within a few miles of water sources.

Why Chemical Immobilization?

Research, zoo applications, conservation and wildlife management programs often require the chemical immobilization of impala. There is also frequently a need for the capture and manipulation of impala for research and in zoos. Over the years, the development of non- and minimally invasive procedures have allowed researchers, veterinarians and management personnel to obtain various forms of biological data without the need to physically handle animals. Certain information, however, can only be obtained by capturing them.⁴ Captures are also important for marking individuals for various types of study.

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 impala, but these still require the initial capture and manipulation of individual animals.^5,6 Live captures are also required in conservation biology for animal translocations, reintroductions or population restocking.

Biological Considerations

Antelope are ruminants belonging to the family Antilocapridae and Bovidae,⁷ and the variety of species on the African continent 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.⁸ Despite this, nearly all antelope are considered large hoofstock. Additionally, all antelope are prey animals, and have evolved with instincts and behaviors intended to help them survive.

All antelope 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. In the case of mortality occurring during capture, this rate is rather easy to measure, while delayed mortality is much more difficult to determine. As a result of their wide biological diversity, each species of antelope has its own anesthesia recommendations and variations of dosages within species because of diverse individual responses to anesthetic agents.^6,7

The effects of immobilization can considerably differ according to the capture methodology employed. In this regard, the research agrees that captures by remote delivery of immobilizing drugs via darting lower an impala’s stress levels (as opposed to other capture methods), thus decreasing the subsequent capture effects.⁶

Drugs Used for Chemical Immobilization of Impala

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

• 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 of Impala: Procedures and Techniques

When chemically immobilizing impala in a zoo setting, less stress 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.⁸

Remote chemical immobilization is usually carried out by approaching impala and shooting a dart from a helicopter, an off-road vehicle, or from the ground. While this significantly reduces stress compared to physical capture methods, it still impacts the animal’s stress levels. Frightened impala will have an increased heart rate, as well as higher levels of cortisol and other stress-related biochemicals.⁵ An approach from the ground tends to produce even lower stress levels, 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 known for their alertness, speed and agility.

Analgesia is essential if the impala’s skin has been breached by anything larger than a hypodermic needle. 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.^4,9 For analgesic drugs, doses and frequencies of administration are more difficult to gauge, even with close observation for discomfort.⁷ 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.⁸

Reversal Agents for Impala

Whether general anesthesia or sedation has been used, reversal agents are often required to neutralize sedation or anesthetic agents. These drugs allow the impala 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 will 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.⁸

Conversely, injectable anesthetics and sedatives (which may be used for less invasive 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 This is where reversal drugs are needed to bring about the desired effect.

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.

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

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.^4,5

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.

The drug formulations currently available for immobilizing impala and other large wildlife species have been refined to a degree that eliminates much of the risk that existed until fairly recently. With the right drug formulations, proper planning and safety precautions, experienced personnel can have the expectation of effective and safe chemical immobilization of impala.

¹ucsd.edu.

²britannica.com.

³awf.org.

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.

⁹Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014.

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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