Bongo Antelope Sedation
Bongo (Tragelaphus eurycerus) are large, forest-living antelopes that are noted for their striking reddish-brown coats with 10-15 vertical white stripes and a thin mane along their back. There are two sub-species of bongo: the Lowland bongo (the Western bongo), and the Mountain bongo (the Eastern bongo). Bongo have large ears and a long, prehensile tongue. Their horns spiral into one or one-and-half twists, with the horns of males being longer. They are the only tragelaphids in which both sexes have horns.
Bongo antelope are found in the lowland forests of Zaire and West Africa to southern Sudan, with small populations in the highland forests of Kenya and also in the Congo. They prefer areas of forest and clearings with fresh vegetation. In East Africa, they are often found in areas with mass bamboo die-offs. The bongo is generally nocturnal, shy and elusive, disappearing into the forest when they feel threatened.
The Lowland bongo is classified by the International Union for Conservation of Nature (IUCN) as Near Threatened (NT), while the Mountain bongo is classified as Critically Endangered (CR).
Anesthesia vs. Sedation
A variety of conservation and wildlife management needs can call for the handling of wild bongo. In such instances, biologists, wildlife managers and/or veterinarians must determine the proper mode of anesthesia and/or sedation. These determinations are largely predicated upon the type of procedure(s) required. For example, marking or blood draws are minimally invasive and require mild to moderate sedation, whereas surgery on an injured bongo would require the remote delivery of sedatives followed by general anesthesia.
Anesthesia is defined as a pharmacologically-induced reversible state of amnesia, analgesia, loss of responsiveness, and loss of skeletal muscle reflexes.1 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.2,3 The advantages of sedation over general anesthesia typically focus on patient safety.
Sedation is associated with decreased risk over anesthesia, therefore sedation is often considered in place of general anesthesia whenever possible.1 Until the advent of potent opiates, the pronghorn antelope (for example) was known to be very difficult to safely capture or anesthetize.4 The focus on the use of sedation in exotic animals such as bongo is a direct result of the perception of greater anesthetic risk in these patients, especially in those that are ill or debilitated. Additionally, conditions in the field are often less than ideal, sometimes leading to more unfortunate outcomes in the event of complications.
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 bongo 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
Risks in the Capture and Chemical Immobilization of Bongo
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 believed to be 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 can lead to the collapse of the animal and eventual death.3 Since bongo are prey animals and have evolved with instincts and behaviors gauged to help them survive, this is an inherent risk during capture events of any kind.
Other risks associated with the capture of bongo include aspiration (vomiting), hypothermia, hyperthermia, frostbite, bloat, respiratory depression/arrest and cardiac arrest. Each species of antelope has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.3,4
Disadvantages of sedation can include incomplete elimination of patient movement, patient semi-awareness, and lack of complete analgesia. So, while 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:
- 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 available1
Agents for the Sedation of Bongo Antelope
In general, sedatives produce calmness, loss of aggression and loss of alertness. In this condition, animals are not immobilized fully and can be aroused by various disturbances. Therefore, they are usually used singly for only 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 combined synergistic effect of tranquilizers and anesthetics 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.3
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, including bongo. When combined with an opioid, its effects are synergistic, allowing a reduction of the amount of either drug.4 Effects are variable, from slight decrease in activity to lateral recumbency. These effects are likely related to species variability in response and the varying dose rates suggested for different species/groups. In all cases, patients still react somewhat to handling and other stimuli.1
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.1
Drugs used for the sedation of bongo will vary, largely depending upon the age, sex and size of the individual, as well as 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 that there is more risk to a partially-immobilized animal and to human handlers than there is to a heavily-dosed animal.4,5 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.
1Lennox, A., DVM. Sedation as an Alternative to General Anesthesia in Exotic Patients. Delaware Valley Academy Veterinary News, March, 2010.
2Balko, J. et al. Advancements in Evidence-Based Anesthesia of Exotic Animals. Veterinary Clinics: Exotic Animal Practice, Volume 20, Issue 3, 917 – 928.
3Sontakke, S., et. al. A Manual on Chemical Immobilization of Wild Animals. European Journal of Wildlife Research, 36 pp 34-41.
4Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed.
5Ball, 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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