Sable Antelope Chemical Immobilization
The sable antelope (Hippotragus niger) inhabits the savannah woodlands in southeastern Africa, with isolated populations of sable in Angola, Zimbabwe, northeastern Botswana, Mozambique, the northeastern part of the Caprivi Strip in Namibia and South Africa.1 The sable an “edge” species that favors the woodland/grassland ecotone.2 They are selective feeders with a preference for fresh growth grasses. Sable are water dependent, and are seldom found very far from water sources.
Four subspecies of sable have been identified: H. n. niger, H. n. kirkii, H. n. roosevelti and H. n. variani. Sable bulls have glossy black coats (hence their name) contrasted by white undersides, rump, throat and facial markings. The females and young are a chestnut to dark brown in color. Both male and female sable have large, curved horns, with those of the females being somewhat shorter and less curved.
Sable typically aggregate in herds of 10–30 individuals, but herds sometimes form in numbers of up to 200 on a temporary basis.1 Subadult males, which are driven off as they mature, are sometimes associated with these herds and occasionally form bachelor groups. Like most other antelope, sable are timid but can become aggressive. In particular, the males can become dangerous if sufficiently provoked, and will use their horns to fend off rivals and predators.
Sedation and Anesthesia of Sable
Researchers, wildlife managers and veterinarians in zoo settings often need to immobilize sable to mark them for identification, to provide veterinary treatment or to relocate them from dangerous or overpopulated locations. While “immobilization” references any forced restriction of movement of all or part of an animal’s body,3 chemical immobilization is achieved using drugs which have a range of intended effects. These may involve widespread muscular paralysis while the animal is fully or partially conscious (sedation), to those which produce unconsciousness with lack of sensation (anesthesia).4
Immobilizing large or potentially dangerous wild animals poses significant challenges with risks for both operators and the animals. This is where immobilization via chemical means is useful, since most wild animals will act defensively when cornered or restrained in any manner. An animal’s threshold of tolerance refers to the point at which a trapped animal will become aggressive upon human approach.1 Sable are prey animals, and have evolved with instincts and behaviors gauged to help them survive, and this must be considered in any capture scenario.
Since just about all antelope species are large enough to be difficult to handle, chemical agents (sedatives and/or anesthetics) may be delivered by hand to a restrained sable by using a pole syringe, or a capture gun (either a handgun or along gun). Capture guns are fired by CO2 gas cartridges or with .22 caliber blanks. Darts are loaded through a breech, one shot at a time, and have an effective range of up to 60 yards.3 Remote chemical immobilization is often carried out by approaching sable and shooting a dart from a helicopter, an off-road vehicle, or from the ground.
Depending on the procedure(s) being performed, individual sable may be handled using heavy sedation or general anesthesia (for invasive surgical procedures). Drug choices and combinations must be of proven safety and calculated for the animal’s weight, age, physiological and reproductive status and body condition. According to the literature, each species of antelope has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.4,5
The chemical immobilization of any animal, particularly in the field, carries numerous risks. These include, but are not limited to capture myopathy, hypothermia, hyperthermia, respiratory depression/arrest, aspiration and cardiac arrest. Additionally, if the onset (induction) of anesthesia is slow, the risk of physical injury such as lacerations, limb injuries, head trauma etc. is increased. It is important for personnel in the field to be familiar with animal handling and immobilization techniques, as well as potential emergencies.
Agents Used in Chemical Immobilization
In the United States, the possession and use of drugs used to capture wildlife is governed by federal and state regulations. All drugs currently used to sedate or immobilize wild animals are prescription drugs and must be obtained and administered by or on the order of a licensed veterinarian. This requires a veterinarian must be involved in the process, but it does not mandate that a veterinarian be on site during the immobilization process. Non-veterinarians using prescription drugs should receive adequate training in their use; some drugs (e.g., opioids) are potentially toxic to humans, even through skin exposure. Some of the drugs used chemical immobilization are also classified as controlled drugs, the possession of which requires a U.S. Drug Enforcement Agency registration number, special record keeping, and special storage requirements.5
The classes of immobilizing agents used on sable include:
Tranquilizers/Sedatives: This class of drugs is used primarily in wildlife immobilization as adjuncts to primary anesthetics (e.g., ketamine, carfentanil) to hasten and smooth induction and recovery and to reduce the amount of the primary agent required to achieve immobilization. Valium is used primarily for small mammals as an anticonvulsant adjunct to ketamine anesthesia and it is also an excellent muscle relaxant. The α-adrenergic tranquilizers (e.g., xylazine or Rompun, medetomidine) are potent sedatives and can be completely antagonized.5,6 They are often combined with ketamine, Telazol, or carfentanil. By themselves, they are capable of heavily sedating animals, particularly ungulates, to the point of relatively safe handling. However, animals sedated with these tranquilizers can usually be aroused with stimulation and are capable of directed attack. Caution should always be exercised with such animals.
Paralytic Drugs: These are also known as neuromuscular blocking (NMB) drugs. They are among the earliest drugs used for the chemical immobilization of wildlife. Despite their long history of use, NMB drugs are generally inferior to modern drugs. There are two major deficiencies of NMB drugs:
- NMB drugs have a very low safety margin and dosage errors of only 10% can result in either no effect (underdosing) or death by asphyxia (overdosing). Mortality rates as high as 70% have occurred.3
- NMB drugs are virtually devoid of central nervous system effects because of their inability to cross the blood-brain barrier. Thus, an animal paralyzed with NMB drugs is conscious, aware of its surroundings, fully sensory, and, as such, can feel pain and experience psychogenic stress yet is physically unable to react.
Because of these deficiencies, NMB drugs should be used judiciously.
Dissociative Anesthetics: This group of drugs, which includes ketamine and tiletamine, is characterized by producing a cataleptic state (a malleable rigidity of the limbs) in which the eyes remain open with intact corneal and light reflexes. Ketamine is probably one of the most widely used drugs for wildlife immobilization because of its efficacy and safety. Tiletamine is unavailable as a single product and it is combined in equal proportions with the diazepinone tranquilizer, zolazepam (e.g., Telazol).When used singly, ketamine usually cause rough inductions and recoveries, and convulsions are not uncommon.6 Because of this, they are usually administered concurrently with tranquilizers or sedatives. There is no complete antagonist for ketamine or Telazol.
Opioids: The opioids have been used for animal immobilization since the 1960s and are the most potent drugs available for this purpose. The most commonly used opioid is carfentanil. A major advantage in the use of opioids is the availability of specific antagonists. The potency of opioids, such as etorphine and carfentanil, is both an advantage and disadvantage. The advantage is the reduced volume of drug required for immobilization makes them the only class of drugs capable of remote immobilization of large animals. The disadvantage is that they are potentially toxic to humans, with death being due to respiratory failure. Opioid immobilizing agents should never be used while working alone or without having an antagonist immediately on hand.4
Recovery and Reversal Agents
In sable, the duration of anesthesia is influenced by the drugs used, age, sex, body weight, procedure performed and the amount of stimulus during the procedure. Whether sedation or general anesthesia has been employed, reversal agents are often required to neutralize sedation or anesthetic agents, thus allowing the animal 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.
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.3,4 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 sable. Some of these are available in kit form, which include both the immobilizing and reversal agents.
3Pennfoster.edu. Animal Handling And Chemical Immobilization.
4Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed.
5Nielsen, L. Chemical Immobilization of Wild and Exotic Animals. (1999) Ames, Iowa, Iowa State University Press.
6Stoskopf, M. Handbook of Wildlife Chemical Immobilization. Journal of Wildlife Diseases 2014 50:1, 157-157.
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.
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