Nyala Antelope Chemical Immobilization and Sedation
Research, conservation and management programs often require the capture and manipulation of antelope and other large hoofstock. The development of non- and minimally invasive procedures over the years have allowed researchers, zookeepers, veterinarians and management personnel to obtain certain types of data without the need to handle animals.
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. Live captures are also required in conservation biology for animal translocations, reintroductions or population restocking.
Nyala Biology and Habitats
The nyala is an antelope that is native to Southern Africa and is a species of the family Bovidae and genus Tragelaphus. The nyala’s coat is brown in females and juveniles, but grows a dark brown or grey in mature males. There are two subspecies of nyala: The lowland nyala (Tragelaphus agasi), and the mountain nyala (Tragelaphus buxtoni). Female and young male nyala have ten or more white stripes on the sides. Both males and females have a white chevron between their eyes and a long, bushy tail a white underside. Only the males have spiral horns; these are yellow-tipped and have one or two twists.1
The nyala occupies dense woodlands on the coastal plains and major river valleys of eastern Africa from southern Malawi to Natal and is a cover-dependent browser and grazer.2 Their habitats include lush grasslands next to the cover where these animals spend the day; at night, they emerge to graze during the rainy season. Their habitat requirements are thought to be partly due to the fact that nyala do not have the explosive running ability of many other African antelope. Females and young live in small herds of five or six animals. Male nyala occupy overlapping ranges and are nonterritorial.
The effects of immobilization can differ considerably 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 animal’s stress levels, thus decreasing the subsequent capture effects compared to other techniques.5 This is one of the main reasons why chemical immobilization is becoming the preferred capture method, particularly concerning large mammals like nyala.
Drugs Used for Chemical Immobilization of Nyala
There are three basic classes of central nervous system immobilization drugs that are used on nyala:
- 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 and Methods
In a zoo setting, less stress on an animal is likely to occur than in the field, since zoo animals tend to be far more acclimatized to humans and routine 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 for 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.
Remote chemical immobilization is usually carried out by approaching nyala and shooting a dart from a helicopter, 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.4 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 extremely alert, fast and agile.
Analgesia is essential if the nyala’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.1,6
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.7
Drug Reversal Agents
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.7
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.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.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. 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
Custom Drug Formulations
In light of 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.4 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, since this avoids the undesirable and potentially harmful effects of drugs and facilitates speedy recovery from chemical immobilization events.3,4
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 that was developed for the chemical immobilization of 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 MKBM™ Kit contains:
- 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 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 nyala.
3Brivio 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.
4Powell RA, Proulx G (2003) Trapping and marking terrestrial mammals for research: integrating ethics, performance criteria, techniques, and common sense. ILAR J 44: 259–276.
5Arnemo, 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.
6Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
7Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014.
8Plumb’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.
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