Hypothermia and Hyperthermia in Axis Deer During Capture and Chemical Immobilization

Deer are among the most well-known of the large wildlife species in North America, and they’re popular among hunters and wildlife enthusiasts alike.¹ There are seven species of deer and many sub-species that are native to the continent. Some species of deer in North America have been introduced (non-native), and some interbreeding between species occasionally takes place.

Deer belong to the order Artiodactyla, and to the family Cervidae. Cervids differ from other ruminants in that males grow antlers that are comprised of bone, which are shed and regrown annually. The deer family is further divided into two groups—Old World deer (subfamily Cervinae) and New World deer (subfamily Capreolinae). The difference reflects where these animals evolved, but is not a geographical one. Instead, it references the differing foot structures of the two subfamilies.^1,2

The Axis deer (Axis axis, also known as the spotted deer or chital deer) is a deer species that is native to the Indian subcontinent. It is a fairly large, spotted deer that was introduced into the southwestern U.S. (primarily Texas and several other states) in the early 1900s. Axis deer prefer sparse forested areas with adequate water and shade, tending to avoid rugged terrain. Their food consists largely of grasses.^2,3

Axis deer are highly social, and usually are found in herds ranging from a few animals to more than 100. Herd leaders are usually mature, experienced does. Unlike native North American deer, adult male Axis deer are normally found living with herds of young and old animals of both sexes. Like elk, rutting male Axis deer emit bugle-like bellows, and both sexes can generate alarm calls when threats are present.⁴

The reproductive behavior of Axis deer is similar to that of domestic cattle. In the wild, mature bucks in rutting condition may be found throughout the year, with each buck apparently having an independent reproductive cycle of its own; this may not be synchronized with that of other bucks in the herd.³ Females undergo estrous cycles throughout the year, with each cycle lasting approximately three weeks. While pregnant females may be found year-round, most breeding lasts from mid-May through August.

Only one Axis deer fawn is produced after a 210 to 240-day gestation period. In Texas, fawns are born in early January to mid-April, although they may arrive in any season. Fawns begin consuming green forage by 5 weeks of age, and are weaned at 4 to 6 months.⁴

Stress, Hypothermia and Hyperthermia in Axis Deer

Capturing wild deer of any species—native or introduced—is a highly stressful event which can cause capture-induced hypothermia or hyperthermia. Either of these complications can result in morbidity or mortality. The severity of 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.⁵ 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.⁶

The average body temperature for Axis deer is 101.4°F (38.5°C), with 105°F (40.6°C) being the threshold for hyperthermia.⁷ When these exceed more than 2 to 3 degrees higher or lower than the norm during an immobilization event, there is cause for concern and intervention may be required.^6,7 In the case of capture-induced hypothermia, outward signs may also be evident (see below).

Preventing Hypothermia and Hyperthermia in Axis Deer

When immobilizing Axis deer, constant monitoring of body temperature is essential. Thermometers should be able to read over a wide temperature range, and thresholds should be established before the capture so proper treatment can take place should body temperatures rise or fall to unacceptable levels.

In small animals, hypothermia is more common due to the large surface area-to-volume ratio, but instances of both hypothermia and hyperthermia have both been reported during the capture of nearly all deer species. Some drugs used in chemical immobilization suppress normal thermoregulatory mechanisms, thereby giving rise to hypothermia or hyperthermia. Hyperthermia however, is also common immediately after immobilization of both captive and free-ranging deer due to excitement and struggling while darting.^5-7

Monitoring core body temperature is essential in Axis deer anesthesia,^5,6 and intubation has been widely recommended for any anesthetized deer that needs to be transported or anesthetized for greater than one hour. Prior to the recent advent of formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents), opioids were the mainstay of deer anesthesia in wildlife and captive care.⁶

One Treatment Option: Cooling Axis Deer

Since capture-induced hyperthermia in Axis deer may be severe, one method recommended for improving their chances for survival is to physically cool captured animals. Recommendations for cooling captured Axis deer include placing the animal in the shade and dousing it with water using portable mist sprayers, followed by rapid intravenous (IV) fluid therapy.⁷ In animals with body temperatures greater than 41°C, cold water enemas and intravenous infusion of cold Ringer’s lactate have been recommended.^6,7

Ice packs have been reported to restore the body temperature of hyperthermic deer to pre-capture levels.⁵ The authors referencing this method point out that since carrying water is far less cumbersome and difficult than transporting and maintaining ice-packs in the field, water-dousing may be the most practical and effective first intervention for cooling deer with capture-induced hyperthermia.

Treating Hypothermia in Axis Deer

During sedation/anesthetic events, hypothermia is a common adverse effect in many species. In particular, smaller animals are susceptible to hypothermia during anesthetic events, but large hoofstock and even carnivores can be affected.⁵Thus, 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.

Apart from abnormally low body temperature, signs of hypothermia can include:

• Shivering
• Stiff muscles
• Pale gums
• Fixed, dilated pupils
• Low heart and breathing rates

Shivering may be the only outward symptom in cases of mild hypothermia. As the condition increases in severity, the other symptoms usually become evident. The animal’s vital signs are likely to become increasingly erratic as its body goes into heat conservation mode.^5,8 At this point, the deer’s focus is on keeping its vital organs working by restricting the blood flow from all other parts of the body.

Water bottles filled with warm water and placed around the deer’s body can be helpful in reversing hypothermia. 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.⁹ Returning the animal to a warm environment (if possible) and/or using heat lamps (if available) can also be helpful in this regard.

¹safariclub.org.
²J. Schmidly, J., Bradley, R. The Mammals of Texas, Seventh Edition 1994, University of Texas Press.
³tsusinvasives.org.
⁴animalia.bio.
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.
⁹Wolfe L.L., et. al. Immobilization Of Mule Deer With Thiafentanil (A-3080) Or Thiafentanil Plus Xylazine. J Wildl Dis. 2004;40(2):282-287.