Hypothermia and Hyperthermia in Antelope During Chemical Immobilization

Antelope are very widespread animals, comprising around 90 of the approximately 140 known species of the Bovidaefamily (which includes sheep, goats, and domesticated cattle). Antelope belong to the order Artiodactyla, the most distinctive feature of which is their even number of hooves. The pronghorn antelope, Antilocapra americana, is the only member of the Antilocapra family, with other antelope belonging to the Bovidae family.¹

According to the available literature, each species of antelope has its own anesthesia recommendations. Many species have been reported as 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, the pronghorn antelope was nearly impossible to safely capture or anesthetize.¹

Stress, Hypothermia and Hyperthermia

The capture of wild animals 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.² It has also been called one of the primary indications for the development of capture myopathy.

The mechanisms underlying the increase in body temperature during capture-induced hypothermia and hyperthermia are not fully understood, but one factor appears to be the sympathetic stress response. Even with animals engaging in low levels of activity during capture with mild ambient temperatures can develop severe hyperthermia.³

The average body temperature for pronghorn antelope is 37^o C; most other antelope species typically average between 35^o -42^o C.^1,6 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 (see below).

Preventative Measures

Measurement of 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. Some 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.^1-4

Monitoring core body temperature is essential in antelope anesthesia,^3,5 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.³

Treating Hyperthermia in Antelope

Given that capture-induced hyperthermia in some antelope may be severe, one method recommended for improving their chances for survival is to physically cool captured animals. Recommendations for cooling captured antelope include placing the animals in the shade and dousing them with water using portable mist sprayers, followed by rapid intravenous (IV) fluid therapy.⁴ 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.^3,4

Ice packs were also reported to have restored the body temperature of hyperthermic animals to pre-capture levels.³ The authors point out however, that since carrying water is far less cumbersome and difficult than transporting and maintaining ice-packs in the field, thus they recommend that water-dousing is the most practical and effective first intervention for cooling an antelope with capture-induced hyperthermia.

Treating Hypothermia in Antelope

Hypothermia during anesthetic events is a common adverse effect of anesthesia in many species. In particular, smaller animals are susceptible to hypothermia during anesthetic events, but even large hoofstock and even carnivores can be affected.⁵ Thus, having thermal support available in the form of external heating devices during and after anesthesia is prudent. In general, the time of recovery from anesthesia is typically longer in case of injectable anesthesia rather than inhalant anesthesia.

In addition to 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

With mild hypothermia, shivering may be the only outward symptom. As hypothermia increases in severity, the other usually symptoms become evident. The animal’s vital signs are likely to become increasingly erratic as its body goes into heat conservation mode.^1,3 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 some of the literature states that heating pads should be used with care, as it is easy to burn an animal’s skin.⁴ Returning the animal to a warm environment (if possible) and/or using heat lamps (if available) can also be helpful.

¹Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014.

²Sawicka, J. et. al. Efficacy of Different Cooling Methods for Capture-Induced Hyperthermia in Antelope. (2015).

³Haskins, 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.

⁴Arnemo, 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.

⁵Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007.

⁶Richardson, D. Journal of Mammalogy, Volume 56, Issue 3, 29 August 1975, Pages 698–699.

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