Hypothermia and Hyperthermia in Sable Antelope During Chemical Immobilization
The sable (Hippotragus niger) is one of the most impressive African antelopes. Like other antelope, they are members of the family Bovidae, but are also included in the subfamily Hippotragini. The latter literally means “horse goat”, and designates antelope that resemble horses in their physical attributes and stance.1
The sable is a large antelope which stands around 46–55 inches tall. Bulls weigh in at about 520 pounds, and females at about 480 pounds.2 Sable live in the southern savannas of Africa from the southeastern part of Kenya, in eastern Tanzania, as well as Mozambique to Angola and in southern Zaire, mostly in the Miombo Woodland Zone.1 They prefer a mixture of grassland and savanna woodlands, avoiding open lands where possible.
Four subspecies of sable are currently recognized:
- Black sable (also Mastitis sable)—This is the most widespread sable. Its habitat covers south of the Zambezi River through Zimbabwe and Botswana into South Africa.
- Giant Sable (also Royal sable)—These have the longest horns of any other sable subspecies.
- Common (also southern sable)—This antelope is sometimes called the West Zambian sable.
- Eastern sable—This is the smallest of the sable family, with a range that includes the costal lands of southern Kenya, eastern Tanzania and into Mozambique.2
The pronounced color differences between the sexes make the sable one of the most sexually dimorphic antelope species.2Sable bulls have glossy black coats contrasted by white underparts and facial markings, and boast huge scimitar-shaped horns. Sable females and calves are chestnut in color. South of the Zambezi River, females of the H. niger nigersubspecies are also very dark.
Living in herds of 30 or more animals, sable bulls are very territorial and will fight other bulls for territory and breeding rights. Subadult males are chased out of the herd when they reach three years old, after which they form small bachelor herds; young females typically stay with the main herd. When sable herds encounter predators, the dominant male will stand its ground and use its horns to fight off the threat.1
Hypothermia and Hyperthermia
Chemical immobilization is occasionally necessary for the management of sable, whether in the field, zoo or other settings. Different species of antelope have their own anesthesia recommendations, and some species have a history of being notoriously difficult to effectively anesthetize due to their diverse individual responses to anesthetic agents. It has been widely reported that until the advent of potent opiates, some antelope were nearly impossible to safely capture or anesthetize.3
The capture of sable is a highly stressful event which has the potential to cause capture-induced hypothermia or hyperthermia, either of which can result in morbidity or mortality. The severity of the capture-induced hyperthermia has been associated with the likelihood of organ damage, rhabdomyolysis, alterations in electrolyte balance (possibly leading to dehydration events), increased oxidative stress and death.4 It has also been called one of the primary factors in the development of capture myopathy.
The mechanisms underlying the variances in body temperature during capture-induced hypothermia and hyperthermia are not fully understood, but one factor appears to be the sympathetic stress response.5 The average body temperature for most antelope species averages between 35o -42o C.3,8 When these exceed more than 2 to 3 degrees higher than lower than the norm during an immobilization event, there is cause for concern and intervention may be required. In the case of capture-induced hypothermia, outward signs may also be evident.
Preventing Hypothermia and Hyperthermia
Measurement of an animal’s body temperature should be standard procedure during all anesthetic events, and thermometers should be able to read over a wide temperature range. Hypothermia is more common in small animals because of the large surface area-to-volume ratio, but instances of both hypothermia and hyperthermia have both been reported during the capture of antelope. Certain drugs used in chemical immobilization are believed to suppress normal thermoregulatory mechanisms, thereby causing hypothermia or hyperthermia. Hyperthermia however, is also common immediately after immobilization of both captive and free-ranging antelope due to excitement and struggling while darting.3-6
In antelope anesthesia, monitoring core body temperature is essential,5,7 and intubation has been widely recommended for any anesthetized antelope that needs to be transported or anesthetized for greater than one hour. Until the more recent use of formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents), opioids were the mainstay of antelope anesthesia in wildlife and captive care.5
Treating Hyperthermia in Sable
One recommended method for improving the chances of survival for sable with severe capture-induced hyperthermia is to physically cool captured animals. Recommendations for cooling captured antelope include placing animals in the shade and dousing them with water using portable mist sprayers, followed by rapid intravenous (IV) fluid therapy.6 In animals with body temperatures greater than 41°C, the use of cold water enemas and intravenous infusion of cold Ringer’s lactate has been recommended.5,6
Ice packs have also been reported as restoring the body temperature of hyperthermic animals to pre-capture levels.5 Since carrying water is far less cumbersome and difficult than transporting and maintaining ice-packs in the field, water-dousing may be a more practical and effective first intervention for cooling an antelope with capture-induced hyperthermia.
Treating Hypothermia in Sable
Hypothermia during anesthetic events is a common adverse effect of anesthesia in many species. Smaller animals are particularly susceptible to hypothermia during anesthetic events, but even large hoofstock and carnivores can be affected.7Having thermal support available in the form of external heating devices during and after anesthesia is therefore prudent. Overall, the time of recovery from anesthesia is usually longer in case of injectable anesthesia versus inhalant anesthesia.
Apart from abnormally low body temperature, signs of hypothermia can include:
- Shivering
- Stiff muscles
- Pale or gray gums
- Fixed and dilated pupils
- Low heart and breathing rate
In cases of mild hypothermia, shivering may be the only outward symptom. As hypothermia increases in severity, other symptoms may become evident. The animal’s vital signs are likely to become increasingly erratic as its body goes into heat conservation mode.3,5 At this point, the animal’s focus is on keeping its vital organs working by restricting the blood flow from all other parts of the body.
Hypothermia can be reversed through the use of water bottles filled with warm water and placed around the animal’s body. External heating devices may also be used, although the literature states that heating pads should be used with care, as it is easy to burn an animal’s skin.6 Returning the animal to a warm environment as soon as possible and/or using heat lamps (if available) can also be helpful.
3Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014.
4Sawicka, J. et. al. Efficacy of Different Cooling Methods for Capture-Induced Hyperthermia in Antelope. (2015).
5Haskins, S.C. (1995). Thermoregulation, hypothermia, hyperthermia. In: SJ. Ettinger. & EC. Feldman (Eds), Veterinary internal medicine (4th edition) (pp. 26–30). Philadelphia. U.S.A. W.B Saunders Company.
6Arnemo, J., Fahlman, A. (2008). Biomedical protocols for the free-ranging brown bears, gray wolves, wolverines and lynx. Hedmark University College, Norway and Swedish University of Agriculture Sciences, Sweden.
7Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007.
8Richardson, D. Journal of Mammalogy, Volume 56, Issue 3, 29 August 1975, Pages 698–699.
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