Shock in Sable Antelope During Capture and Chemical Immobilization
The sable antelope (Hippotragus niger) is found in the savannah woodlands in southeastern Africa, with isolated populations in Angola. In southern Africa, they occur in Zimbabwe, northeastern Botswana, scattered subpopulations in Mozambique, the northeastern part of the Caprivi Strip in Namibia and South Africa.1 Four subspecies of sable have been identified: H. n. niger, H. n. kirkii, H. n. roosevelti and the Giant Sable (H. n. variani), in Angola.
The sable is considered an “edge” species that inhabits the woodland/grassland ecotone.2 They are known to be selective feeders, having a preference for fresh growth grasses. Sable are dependent on drinking water, and are seldom found far from water sources.
Both male and female sable have scimitar-shaped horns, with those of the females being shorter and less curved. Sable bulls have glossy black coats contrasted by white undersides, rump, throat and facial markings. The females and young are a chestnut to dark brown in color. Sable occur in herds of 10–30 individuals, but herds occasionally aggregate in numbers of up to 200 on a temporary basis.1 Subadult males, which are typically driven off as they mature, are sometimes associated with these herds and occasionally form bachelor groups.
Like most other antelope, sable are generally timid but can become aggressive. In particular, the males can become dangerous if sufficiently provoked. When herds are threatened by predators (including lions), the dominant males will confront them, and many big cats have been reported as dying during such fights.2
The Dynamics of Shock
Shock is a serious condition that is brought on by a sudden drop in blood flow throughout an animal’s body. It can be the result of a wide variety of circumstances, including extreme physical stress, trauma, disease, heatstroke, blood loss, allergic reactions or severe infection. When an animal is in shock, its organs are not receiving an adequate amount of blood or oxygen.3 If untreated, this can lead to permanent organ damage or death.
The processes surrounding capture and/or chemical immobilization can include extreme physical stress sufficient to induce shock in sable. The degree of risk is dependent upon factors such as species, sex, age, overall health, environment, 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.
There are three main categories of shock:
Circulatory Shock. This 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.3
Hypoxic shock. This results from impaired oxygen delivery to cells.
Metabolic shock. Involves cells that have become unable to utilize oxygen for energy production.
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.3,4
Chemical Immobilization and Shock
Even under ideal circumstances, chemical immobilization carries significant risks. Almost all of the drugs that produce anesthesia endanger cardiovascular stability through the impairment of cardiac function, vascular reactivity and autoregulatory responses.4 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.4 However, if tissues are not adequately perfused with blood, oxygen fails to get to the cells, regardless of the oxygen content in the blood.5
Dramatic changes in the mean arterial pressure (MAP) can trigger changes in heart rate.3,4 An increase in MAP causes bradycardia and vasodilation, while a decrease produces tachycardia and vasoconstriction.4 Venous circulation represents approximately 70% of an animal’s total blood volume, and is a chief contributor to stroke volume and cardiac output.4Vasodilation 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.3 A state of relative hypovolemia can remain clinically undetected for protracted periods of time, depending on factors such as patient status and monitoring.3-5
Diagnosis and Treatment of Shock in Sable
Clinical signs of shock in sable can include any combination of the following:
- Unresponsiveness
- Hypothermia
- Tachycardia
- Bradycardia
- Tachypnea
- Bradypnea
- Marked hypotension
- Cyanosis
- Orthopnea
Increasing oxygen delivery to the tissues is imperative in the treatment of shock in sable. This can be done by providing supplemental oxygen, increasing effective circulating volume, increasing hemoglobin concentration and increasing cardiac output with stimulants.4,6 An intravenous catheter may also be placed for vascular access. 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.7
Fluid therapy in the form of lactated Ringer’s solution, Normosol-R, and Plasma-Lyte are the preferred choices for resuscitation, since these have been shown to cause fewer complications as well as decrease the risk of mortality.1 Hypertonic saline is also a popular option for fluid therapy (increasing vascular volume). This increases plasma osmolarity, pulling water into the vascular space from the interstitial space and expanding plasma volume.3,4
Blood products are an important adjunct for the treatment of shock in sable. In normal animals, anemia can be well-tolerated with oxygen delivery being maintained. In those with trauma and acute loss of blood volume however, the associated stressors can contribute to decreased oxygen delivery.4
4Noel-Morgan, J., Muir, W. (2018) Anesthesia-Associated Relative Hypovolemia: Mechanisms, Monitoring, and Treatment Considerations. Frontiers in Veterinary Science, Vol. 5 (53).
5Haller G, Laroche T, Clergue F. Morbidity in anaesthesia: today and tomorrow. Best Pract Res Clin Anaesthesiology (2011) 25(2):123–32.
6Steadman J, Catalani B, Sharp CR, Cooper L. Life-threatening perioperative anesthetic complications: major issues surrounding perioperative morbidity and mortality. Trauma Surg Acute Care Open (2017).
7Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014,
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