The Bongo (Tragelaphus eurycerus) is the largest of Africa’s forest antelopes. It is nocturnal, and has two subspecies: the western or lowland bongo, and the eastern or mountain bongo. The western bongo is considered threatened and the mountain bongo critically endangered. It is said among some native people that if one eats or touches bongo, they (the person) will have spasms similar to a seizure.Population counts have been difficult to determine, since bongo are secretive animals. Bongo have been known to eat burned wood after lightning storms, a behavior that is believed to be a means of acquiring salt or minerals.1 Normally, they use their prehensile tongue to grasp the vegetation upon which they feed.
Like some deer and elk in the Americas, bongo are excellent high-jumpers, but prefer to go under or around obstacles. In order to swiftly maneuver through the dense forest vegetation, bongos tilt their chin up, causing their horns to lie flat against their back. They take this position so frequently older bongos often have bald spots on their back from the tips of their horns rubbing away the fur.1
The processes surrounding capture and/or chemical immobilization can include extreme physical stress and/or trauma sufficient to induce shock in bongo. The degree of risk is contingent upon factors such as species, sex, age, overall health, environmental factors, length of immobilization, the degree of stress involved in the capture/immobilization event itself, the specific chemical agents involved in immobilizing the animal and others.
Shock in bongo antelope is a critical condition that is brought on by a sudden drop in blood flow throughout the animal’s body. Shock can be the result of a wide variety of conditions or circumstances, including extreme physical stress, trauma, disease, heatstroke, blood loss, allergic reactions or severe infection.2,3 When an animal is in shock, its organs are not receiving an adequate amount of blood or oxygen. If untreated, this can lead to permanent organ damage or death.
The three main categories of shock are circulatory shock, hypoxic shock and metabolic shock. Circulatory shock occurs when there is a decrease in effective circulating blood volume. This category is further divided into the three subcategories of cardiogenic, hypovolemic and distributive shock. Cardiogenic shock occurs when the circulating volume of blood decreases despite normal or increased blood volume. Hypovolemic shock occurs when blood volume is decreased through hemorrhage, third space fluid distribution, or dehydration. Distributive shock occurs when the body is unable to maintain the vasoconstriction of blood vessels.2
Hypoxic shock results from impaired oxygen delivery to cells, while metabolic shock involves cells that have become unable to utilize oxygen for energy production.2-4 For the purposes of this discussion, the types of shock being discussed are the subcategories of circulatory shock and hypoxic shock, which are the most likely to be brought on due to capture and/or immobilization events.
Even under the best and well-controlled circumstances, chemical immobilization in antelope is a risky proposition. Almost all of the drugs that produce anesthesia endanger cardiovascular stability by producing dose-dependent impairment of cardiac function, vascular reactivity and autoregulatory responses.3 Additionally, antelope have a reputation for being difficult to safely immobilize chemically.
Hemoglobin is found within red blood cells and carries oxygen to tissues. Normally, the amount of oxygen delivered to the cell is 2 to 4 times the amount required, depending on the tissue, which ensures an adequate supply.3 However, if tissues are not adequately perfused with blood, the oxygen fails to get to the cells, regardless of the oxygen content in the blood.4
Venous circulation represents approximately 70% of an animal’s total blood volume, and is a chief contributor to stroke volume and cardiac output.4 Vasodilation is the primary cause of hypovolemia produced by anesthetic drugs. It is often associated with increased venous compliance, decreased venous return, and reduced response to vasoactive substances.1Depending on things like patient status and monitoring, a state of relative hypovolemia can remain clinically undetected for protracted periods of time.2-4
Clinical signs of shock in bongo antelope can include any combination of the following:
Treatment of shock must focus on increasing oxygen delivery to the tissues. This can be accomplished by providing supplemental oxygen, increasing effective circulating volume, increasing hemoglobin concentration and increasing cardiac output with stimulants.2,4 If possible, an intravenous catheter should be placed for vascular access. If venous access cannot be established, an intraosseous catheter can be placed. Oxygen supplementation, when available, will also provide benefits to the animal experiencing shock. This can be accomplished via flow-by oxygen, mask, nasal cannulas or an oxygen cage.5
Lactated Ringer’s solution, Normosol-R, and Plasma-Lyte are the preferred choices of fluid therapy for resuscitation, as these have been shown to cause fewer complications as well as decrease the risk of mortality2 as compared to other options. Hypertonic saline is also a popular option for fluid therapy (increasing vascular volume). Hypertonic saline increases plasma osmolarity, pulling water into the vascular space from the interstitial space, thereby expanding plasma volume. It should be noted that hypertonic saline has unwanted side effects, such as a transient, dose-dependent increase in sodium and chloride will occur.2,3
Finally, blood products are an important adjunct for the treatment of shock. In normal patients, anemia can be well-tolerated with oxygen delivery being maintained. In antelope with trauma and acute loss of blood volume however, the associated stressors can contribute to decreased oxygen delivery.3
1Estes, Richard D. The Behavior Guide to African Mammals: Including Hoofed Mammals, Carnivores, Primates. Berkeley and Los Angeles: University of California Press., 1991.