The bongo is a large forest-living antelope that lives in the lowland forests of West Africa to southern Sudan, with small populations occupying some highland forests of Kenya and the Congo. Bongo have a reddish-brown coat with 10-15 vertical white stripes and a thin mane running along their back. Their horns spiral into one or one-and-half twists, with the horns of the males being longer. There are two sub-species of this antelope: the Lowland bongo (or Western bongo) and the Mountain bongo (or Eastern bongo).
Field immobilization of bongo is sometimes required for medical examination, blood sample collection, and animal identification, and the importance of performing such procedures for research and conservation projects is widely acknowledged.1 Research in this area itself has revealed that the physiological and behavioral effects of capture are as important as the direct risks of injury or death of an animal.2
There are a number of common stressors attendant to the chemical immobilization of antelope that can, in some cases, lead to complications during or after an anesthetic event. The overall health of an individual animal (which might be poor, and in some cases the very reason for its capture) is also a factor affecting the potential for complications during and after anesthesia.
Chemical immobilization represents a chemically-induced stressor, although other stressors are often included in immobilization events. The physical stress of capture and/or attempts to escape during capture on the part of an animal certainly constitute physiological stress; surgical and even environmental conditions can bring about physical stress, and anxiety and fear are nearly always a component to some degree in a capture scenario.
The effects of acute stress during capture can include spikes in adrenaline, cortisol levels, heart rate, blood pressure, respiration, metabolic rate, blood glucose, lactic acid and body temperature, while bringing about a decrease in pH and a redistribution of blood within the organs.3 The effects of capture and anesthesia can activate the fight-or-flight response, HPA-axis activation, hyperthermia, respiratory depression (hypoxemia), lactid acid build-up, acidosis; in severe cases, this can lead to neurological/myocardial dysfunction, multi-organ failure, capture myopathy and death.4
The available literature states that each species of antelope has its own anesthesia recommendation with intra-species variations of dosages because of diverse individual responses to anesthetic agents.2,3 These variations are of course factors in the risk of complications in these species, and attendant factors must also be taken into account. Prior to the advent of some of the newer drug formulations, some antelope species were known to be notoriously difficult to immobilize successfully.
Dehydration (a reduction of the body’s water content) may not seem like a major concern compared to other potential complications, but inasmuch as it can lead directly to cardiac arrest, dehydration is potentially very dangerous. This comes about as a factor of essential electrolytes being depleted as the water content in an animal diminishes (see below). If an animal loses more water and electrolytes than it is taking in, it will begin to dehydrate and its health will quickly deteriorate.
Electrolytes are minerals that naturally occur in all animals, and they are essential for proper health. Electrolytes are comprised of sodium, chloride, and potassium, and facilitate the movement of nutrients into cells, aid in muscle function, and help regulate nerve activities.3,4 An animal’s natural activities—breathing, urinating, and defecating, as well as simple evaporation—can all cause it to lose fluids. When an animal eats and drinks, the lost water and electrolytes are replaced. If the animal’s fluid intake becomes less than what they are losing, dehydration will occur. This causes a reduction in bodily fluids that reduces blood flow and the delivery of oxygen to organs and tissues.
To understand dehydration, one must first understand the distribution of fluid and water in the body. Total body water (TBW) comprises approximately 60% of an animal’s body weight. Approximately 67% of TBW is found inside the body’s cells; this is referred to as intracellular fluid (ICF). The remaining 33% of TBW is the extracellular fluid (ECF), which comprises:
Dehydration can be caused by hyperthermia, chronic vomiting or diarrhea, excessive urination or wound drainage. Due to the stressful nature of capture and chemical immobilization events, they have been known to bring about dehydration. In both human and veterinary practices, IV fluids are usually administered prophylactically, depending on the nature of the procedure. Veterinarians often provide fluid therapy to patients for many reasons, including correction of dehydration, expansion and support of intravascular volume, correction of electrolyte disturbances, and encouragement of appropriate redistribution of fluids that may be in the wrong compartment (e.g., peritoneal effusion).2
During immobilization events, the animal’s hydration status can be assessed using various tests. One of the easiest to perform is a skin tent test to check the turgor (moisture level) of the skin. To do this, the skin over the thorax or lumbar region is pulled away from the back. In a well-hydrated animal, the skin immediately returns to its normal resting position. If the tent formed remains standing, it is a likely indication of dehydration. If there is evidence of dehydration in an antelope during a procedure, all administration of immobilizing drugs must be immediately suspended. Fluid therapy should begin in the form of lactated Ringer’s solution or 0.9% saline, IV, SQ or IP.3
Perioperative IV fluid therapy is very common in veterinary medicine and allows practitioners to restore intravascular volume, correct dehydration, and administer IV medications quickly.4 While perioperative fluid therapy under many field conditions may be impractical, fluids should always be available in the case of dehydration when chemically immobilizing antelope.
1Laricchiuta P, De Monte V, Campolo M, Grano F, Iarussi F, Crovace A, Staffieri F. Evaluation of a butorphanol, detomidine, and midazolam combination for immobilization of captive Nile lechwe antelopes (Kobus magaceros). J Wildl Dis. 2012 Jul;48(3):739-46.