Sedation in Impala Antelope
The impala (Aepyceros melampus) is a medium-sized antelope inhabiting the bushveld regions of South Africa and the savannas of eastern and southern Africa, and is the most common antelope in these areas. Impala are reddish-brown in color with lighter undersides. They have black markings on the hips and tail, white markings above each eye, under their chin and on the underside of their tails.
Impala are fast runners and can leap distances up to 30 feet to escape predators, and often bound as high as 10 feet into the air to clear obstacles. They are also known to be very vocal; the males make loud vocalizations while rutting, and all impala emit loud warning snorts if danger is present.1,2
Impala are both diurnal and nocturnal. They are usually most active immediately after sunrise and just before sunset. Female impalas and their offspring gather into herds which number from 15 to 100 individuals. A herd’s home range 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.
Breeding activity for impala spans from March through May. Impala have a polygynous mating system, with each male mating with a number of females during each breeding season.2 During this time, pregnant females live in isolation to give birth. After gestating from 190 to 200 days, a single calf is born, following which the mother and calf rejoin the herd.3
For food, impala browse and graze, feeding upon grasses, fruit and leaves. They also tend to inhabit areas close to water sources. The chief predators of impala are leopards, lions, jackals and caracal.
Anesthesia vs. Sedation in Impala
For the purpose of definition, “anesthesia” is a pharmacologically-induced, reversible state of amnesia, analgesia, loss of responsiveness, and loss of skeletal muscle reflexes. 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.4
The advantages of sedation over general anesthesia often focus on patient safety. The comparative safety of sedation over general anesthesia in human and animal patients is well-established. Sedation is associated with decreased risks over anesthesia, therefore, sedation is often considered in place of general anesthesia whenever possible. Until the advent of potent opiates, some antelope species were known to be very difficult to safely capture or anesthetize.4 The focus on the use of sedation in exotic animals such as impala is a direct result of the perception of greater anesthetic risk in these animals, especially in those that are ill or debilitated.
Additional advantages of sedation include general reduction of anxiety and stress related to disease processes such as respiratory disease, and for diagnostic sampling and therapeutics. Sometimes 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.4,5
Capture and Chemical Immobilization Risks
The term “chemical immobilization” encompasses both anesthesia and sedation. Numerous physiological and metabolic changes occur as a result of chemical immobilization, and not all of these are directly caused by the immobilizing agents. Some of these changes are biochemical, and the most serious of these 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. It leads to the collapse of the animal and eventual death from acidosis, predation or other factors.6 Since impala are prey animals that have evolved with instincts and behaviors to help them survive, this is an inherent risk in impala capture events.
Other risks associated with the capture of antelope include vomiting and aspiration, hypothermia, hyperthermia, frostbite, bloat, respiratory depression/arrest and cardiac arrest.6,7
There are disadvantages to sedation (versus anesthesia) which can include incomplete elimination of patient movement, patient semi-awareness, and lack of complete analgesia. Therefore, 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 when procedures are expected to produce discomfort.6
The American College of Veterinary Anesthetists (ACVA) has published recommendations for monitoring animals that are sedated without general anesthesia:
- Palpation of pulse rate, rhythm and quality
- Observation of mucous membrane color and CRT
- Observation of respiratory rate and pattern
- Pulse oximetry Supplemental oxygen, and endotracheal tube (where applicable) and materials to obtain vascular access should be readily available4
Agents for the Sedation of Impala
Sedatives produce calmness, loss of aggression and loss of alertness which are generally required for purposes such as transportation. In this condition, animals are not immobilized fully and can be aroused by various disturbances. Therefore, they are usually used singly for only 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. The synergistic effect of tranquilizers and anesthetics is far greater than the individual effect of single drugs with respect to smooth induction, good muscle relaxation and smoother recovery.6
Sedatives commonly used in veterinary medicine include 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 by blocking dopamine receptors within the brain, thereby depressing certain brain functions.6
Midazolam is used in human and veterinary medicine for pre-anesthesia and sedation. It 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.4 Effects are variable, and are likely related to species variability in response and the varying dose rates suggested for different species/groups. In all cases, patients still react to a limited degree to handling and noxious stimuli.4
When midazolam is used singly, sedation may or may not 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.
Drugs used for the sedation of impala will vary, largely depending upon the preference and experience of the veterinarian or wildlife management personnel. The available literature often suggests that dosing higher when in doubt is in fact far safer than dosing conservatively. In the latter case, there is more risk to a partially-immobilized animal and to human handlers than there is to a heavily-dosed animal.7,8 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 or life at risk.
4Lennox, A., DVM. Sedation as an Alternative to General Anesthesia in Exotic Patients. Delaware Valley Academy Veterinary News, March, 2010.
5Balko, J. et al. Advancements in Evidence-Based Anesthesia of Exotic Animals. Veterinary Clinics: Exotic Animal Practice, Volume 20, Issue 3, 917 – 928.
6Sontakke, S., et. al. A Manual on Chemical Immobilization of Wild Animals. European Journal of Wildlife Research, 36 pp 34-41.
7Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed.
8Ball, 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.
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