Hypothermia and Hyperthermia in Barasingha Deer During Capture and Chemical Immobilization

The barasingha deer (Rucervus duvaucelii), also called the swamp deer, belongs to the family Cervidae (order Artiodactyla). Typically found in wet areas near grasslands in India and Nepal, it is one of the most widely-recognized species in its native range. The barasingha deer differs from other deer species in India in that its antlers often have many more than three times. It is from this feature that the deer gets its name, which loosely translates into "twelve-horned" in Hindi.¹

The total population of barasingha deer was estimated at less than 4,000 individuals in India and Nepal in the late 1960s. These losses were primarily due to overhunting, disease and the conversion of large grassland areas into cropland.² Today, there are fragmented populations in northern and central India, and the barasingha has been introduced into several countries.^2,3 In the U.S., this deer may be hunted on carefully-controlled ranches and reserves.

The barasingha deer is relatively large, with a shoulder height of approximately 45 inches and an overall length of nearly 6 feet. Stags usually weigh from 350 to 630 lbs., and females weigh from 290 to 320 lbs. Larger stags have been reported as weighing up to 570 lbs.¹ The barasingha deer’s coat is yellowish-brown and wooly, with white spots along its spine. Its throat, abdomen, inside of the thighs and beneath the tail is white, and its coat becomes a brighter orange-brown color in summer. The females are a bit paler in color than males, and the young have faint spots.²

Barasingha deer are grazers, with a diet primarily consisting of grasses and aquatic plants. During the day, they feed during the mornings and late afternoons. In India, herds comprise from 8 to 20 individuals, and larger herds may have up to 60 individuals. During the rut, barasingha deer form large herds of adults. Their breeding season lasts from September to April, and fawns are born after a gestation period of approximately 245 days in August through November.^3,4

Hypothermia and Hyperthermia Risks in Barasingha Deer

Capture-induced hypothermia and hyperthermia are serious complications in that either of these 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 indicators for the development of capture myopathy, a deadly complication.

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.⁵

The average body temperature for barasingha deer is 101.4°F (38.5°C), with 105°F (40.6°C) being the threshold for hyperthermia.⁶ 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.⁷ In the case of capture-induced hypothermia, outward signs may also be evident (see below).

Preventing Hypothermia and Hyperthermia in Barasingha Deer

The constant monitoring of body temperature is essential when immobilizing large hoofstock such as barasingha deer. Thermometers should be able to read over a wide temperature range, and thresholds should be established before the capture so that proper treatment can take place when body temperatures rise or fall to unacceptable levels.

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 deer. 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 barasingha deer due to excitement and struggling while darting.^4-8

Monitoring core body temperature is essential in 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. 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 deer anesthesia in wildlife and captive care.³

Treating Hyperthermia in Barasingha Deer

Given that capture-induced hyperthermia in some deer may be severe, one method recommended for improving their chances for survival is to physically cool captured animals. Recommendations for cooling captured deer include placing the 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.^6,7

Ice packs have been reported to restore the body temperature of hyperthermic animals to pre-capture levels.⁶ Since carrying water is far less cumbersome and difficult than transporting and maintaining ice-packs in the field however, water-dousing may be a more practical and effective first intervention for cooling deer with capture-induced hyperthermia.

Treating Hypothermia in Barasingha Deer

Hypothermia during immobilization events is a common adverse effect of sedation/anesthesia in many species. Smaller animals tend to be more susceptible to hypothermia during anesthetic events, but large hoofstock and even carnivores can be affected.⁵ Thus, having thermal support available (e.g., external heating devices) during and after the sedation or anesthesia of barasingha deer is prudent. The time of recovery from anesthesia is typically longer in case of injectable anesthetics than with inhalant anesthesia.

Apart from an 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, the deer’s 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.^5,8 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 deer’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.⁶ Returning the animal to a warm environment and/or using heat lamps (if available) can also be helpful.