The word “antelope” is used to describe a wide variety of horned mammals in the Families Bovidae and Antilocapridae. Antelope males and the females of some species have unbranched horns that attach to the frontal bones of the skull.The sable antelope (Hippotragus niger) is one of Africa’s most visually remarkable antelopes. It is a member of the “horse antelope” subfamily (Hippotragini) due to its compact, sturdy build and stance which give it a horse-like appearance.1
Sable bulls have glossy black coats contrasted by white undersides, rump, throat, facial markings and large scimitar-shaped horns. Its horns and striking appearance have made this antelope a favorite among trophy hunters. Both male and female sable have horns, although those of the females tend to be slightly shorter and less curved. The females and young are a chestnut to dark brown in color; in the H. niger niger subspecies which inhabit areas south of the Zambezi River, females can appear very dark.
The range of the sable includes the southern savanna from central Tanzania to South Africa.2 It is an “edge” species that favors the ecotone between wooded savanna and grassland. From September to April (the rainy season), sable forage grasses and foliage of the woodlands; during the dry season, they come out onto grasslands where it grazes on green plants that emerge after the annual fires. Sable are water-dependent and visit pools daily during the dry season.1
The sable is territorial but highly sociable. Herds of females and young of over 50 animals congregate in ranges of 4 to more than 20 square miles. In some areas, these can number in the hundreds. Female offspring generally remain in the home range, but established adult males drive out subadult males as they mature. These young males typically join bachelor herds until they are ready to compete for their own territory.2
Anesthesia is a drug-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. Often, the advantages of sedation over general anesthesia typically focus on patient safety.
The comparative safety of sedation over general anesthesia in human patients is well established. Sedation is associated with decreased risk in other species as well; therefore, sedation is often considered in place of general anesthesia for minor surgical and other procedures.1 Until the advent of potent opiates, some antelope species were known to be very difficult to safely capture or anesthetize.3 The focus on the use of sedation in exotic animals such as sable is a direct result of the perception of greater anesthetic risk in these patients.
Additional advantages of sedation include a 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 must be weighed against the risk of foregoing diagnostic testing or procedures, or the risk of general anesthesia. For these patients, sedation provides an attractive alternative.3
“Chemical immobilization” includes 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 come about as the result of capture, the most serious of which can bring about a condition called capture myopathy. This is 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. This leads to the collapse of the animal and eventual death from acidosis, predation or other factors.4,5 Since sable are prey animals and have evolved with instincts and behaviors designed to help them survive, this is an inherent risk in capture events.
Other risks associated with the capture of sable 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 their diverse individual responses to anesthetic agents.4
Disadvantages of sedation can include incomplete elimination of patient movement, patient semi-awareness, and lack of complete analgesia. 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.5 The American College of Veterinary Anesthetists (ACVA) has published recommendations for monitoring animals that are sedated without general anesthesia (ACVA recommendations):
In general, sedatives produce calmness and a loss of alertness, both of which are required during transportation. In this condition, animals are not fully immobilized and can be aroused by various disturbances. As such, they are typically 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 combined synergistic effect of tranquilizers and anesthetics is far greater than the effect of either of the two drugs used singly with respect to smooth induction, good muscle relaxation and smoother recovery.5
Sedatives 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.5
Midazolam is often used for pre-anesthesia and sedation and has a wide margin of safety in many species. When combined with opioids, its effects are synergistic, allowing a reduction of the amount of both drugs.6 Effects are reportedly variable, from slight decreases 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 may still react somewhat to handling and noxious stimuli.3
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. If additional immobilization is essential, low concentrations of inhalant gas can be considered.3
Drugs used for the sedation of sable will vary, largely depending upon the preference and experience of the veterinarian or wildlife management personnel. The 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.6,7 This is largely due to the relative safety of modern drug formulations, which allow for much more latitude in dosing without increased safety risk.
1britannica.com.