Nyala Antelope Sedation
Antelopes encompass a wide variety of horned mammals in the Families Bovidae and Antilocapridae. Antelope males and the females of some species have unbranched horns that attach to the frontal bones of the skull.Antelope vary widely in size; the royal antelope weighs an average of about four pounds, whereas the eland weighs up to 1,800 pounds. Despite being extremely widespread in geography and diverse in size, behavior and habitats, most antelope are considered to be large hoofstock.
Nyala are a shy antelope species that inhabit areas of dense thicket and forest in southern parts of Africa.1 There are two subspecies of nyala: The lowland nyala (Tragelaphus agasi), and the mountain nyala (Tragelaphus buxtoni). These herbivores will eat shrubs, fruit, leaves and grass, and spend much of their time grazing. Since nyala dwell at the fringes of forests and do not possess the running speed of other African antelope, they are one of the most alert antelope species. They sense danger using exceptional hearing, smell and sight.
Male nyala grow an impressive pair of spiral horns; these twist 1.5 to 2.5 times and may measure 24-33in (60-83cm) long.1,2 Female nyala do not have horns. Male nyala have a coarse, dark grey coat and pale stripes on their torsos. Females and juveniles are reddish-brown and have 10 prominent white stripes on the sides of their bodies.
Anesthesia vs. Sedation
Anesthesia is defined as a pharmacologically induced reversible state of amnesia, analgesia, loss of responsiveness, and loss of skeletal muscle reflexes.3 In contrast, sedation is a drug- induced depression of consciousness during which an animal cannot be easily aroused, but may respond following repeated or painful stimulation. The advantages of sedation over general anesthesia typically focus on patient safety.
The comparative safety of sedation over general anesthesia in human patients is well established. Sedation is associated with decreased risk in other species as well; therefore, sedation is often considered in place of general anesthesia whenever possible.3-5 Until the advent of potent opiates, the pronghorn antelope (for example) was known to be very difficult to safely capture or anesthetize.6 The focus on the use of sedation in exotic animals such as nyala is a direct result of the perception of greater anesthetic risk in these animals, particularly those that are ill or debilitated.
Other advantages of sedation include general reduction of anxiety and stress related to disease processes such as respiratory disease, and for diagnostic sampling and therapeutics. In some cases, the risk of handling must be weighed against the risk of foregoing diagnostic testing or procedures, or risk of general anesthesia. For these animals, sedation provides an attractive alternative.1
Capture and Chemical Immobilization Risks
The term “chemical immobilization” covers both anesthesia and sedation. There are many physiological and metabolic changes that occur as a result of chemical immobilization, not all of which are caused by the immobilizing agents. Many of these changes are due to the capture of the animal itself, the most serious of which can bring about a condition called capture myopathy. This is related to a metabolic acidosis caused by extreme exertion over a short period of time, resulting in necrosis of the large muscle masses of the legs and other areas.3,4 Since all antelope are prey animals and have evolved with instincts and behaviors gauged to help them survive, this is an inherent risk in nyala capture events.
Other risks associated with the capture of antelope include aspiration (vomiting), hypothermia, hyperthermia, frostbite, bloat, respiratory depression/arrest and cardiac arrest.
Disadvantages of sedation can include incomplete elimination of patient movement, patient semi-awareness, and lack of complete analgesia. Thus, while the drugs and lower dosages used for sedation are linked with greater patient safety, they are not entirely without risk. These disadvantages can be overcome with careful dosing and monitoring, effective patient handling and efficient use of analgesics when handing or procedures are expected to produce discomfort.3 The American College of Veterinary Anesthetists (ACVA) has published recommendations for monitoring animals that are sedated without general anesthesia (ACVA recommendations):
- Palpation of pulse rate, rhythm and quality
- Observation of mucous membrane color and CRT
- Observation of respiratory rate and pattern
- Auscultation
- Pulse oximetry Supplemental oxygen, and endotracheal tube (where applicable) and materials to obtain vascular access should be readily available3
Drugs Used for the Sedation of Nyala
Sedatives produce calmness and loss of aggression and alertness which are required during transportation and some medical/management procedures. In this condition, animals are not fully immobilized and can be aroused by various disturbances. Therefore, sedatives are usually used singly for very minor procedures, or as adjuncts to dissociative anesthetics for hastening smoother induction and to reduce the quantity of anesthetic for achieving more effective immobilization.4,5 The synergistic effect of tranquilizers and anesthetic is far greater than the individual effect of either of the two drugs with respect to smooth induction, good muscle relaxation and smoother recovery.3
Sedatives commonly used in veterinary medicine include drugs such as midazolam, alprazolam, amitriptyline, buspirone, clomipramine, dexmedetomidine, diazepam, fluoxetine, lorazepam, paroxetine, sertraline, or trazodone. Acepromazine is also widely used in veterinary medicine as a sedative. It is a member of the phenothiazine class of sedatives and works primarily by blocking dopamine receptors within the brain, thereby depressing certain brain functions.5
Midazolam is often used in human and veterinary medicine for the purposes of pre-anesthesia and sedation and has a wide margin of safety in many species. When combined with an opioid, its effects are synergistic, allowing a reduction of the amount of either drug.6 Dosages most commonly used are 0.5-10 mg/kg, combined with an opioid (butorphanol, buprenorphine, hydromorphone, other). Effects are variable, from slight decrease in activity to lateral recumbency. In all cases, patients can still react minimally to handling and noxious stimuli.3
When midazolam is used alone, sedation may be adequate in ruminants, camelids and several other species. When used in combination with other drugs (e.g., opioids, ketamine, acepromazine, dexmedetomidine), midazolam provides more reliable sedation. It should be noted that use of sedation and manual restraint alone is inappropriate for any procedure expected to produce discomfort. In mammals, additional sedation can be provided with sub-anesthetic dosages of ketamine, 2-7 mg/kg, or alfaxalone, 1 mg/kg IM. If additional immobilization is essential, low concentrations of inhalant gas can be considered.3
Drugs used for the sedation of nyala will vary depending upon the preference and experience of the veterinarian or wildlife management personnel. The available literature suggests that dosing higher when in doubt is in fact far safer than dosing conservatively, in that there is more risk to a partially-immobilized animal and to human handlers than there is to a heavily-dosed animal.6,7 This is largely due to the relative safety of modern drug formulations, which allow for much more latitude in dosing without putting an animal’s health at risk.
3Lennox, A., DVM. Sedation as an Alternative to General Anesthesia in Exotic Patients. Delaware Valley Academy Veterinary News, March, 2010.
4Balko, J. et al. Advancements in Evidence-Based Anesthesia of Exotic Animals. Veterinary Clinics: Exotic Animal Practice, Volume 20, Issue 3, 917 – 928.
5Sontakke, S., et. al. A Manual on Chemical Immobilization of Wild Animals. European Journal of Wildlife Research, 36 pp 34-41.
6Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed.
7Ball, 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.
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