Hypothermia and Hyperthermia in Eld’s Deer During Capture and Chemical Immobilization

Deer are among the most well-known of the large wildlife species, and they’re popular among hunters and wildlife enthusiasts alike. Deer belong to the order Artiodactyla, and the family Cervidae; as such, they are known as cervids. These graceful animals live on almost every continent on the globe; there are around a half dozen species that are common in North America, as well as subspecies and species introduced from other countries.

Cervids differ from other ruminants in that males grow antlers that are comprised of bone. These are shed and regrown annually, and increase each year in size and intricacy. Except in the case of caribou, female deer do not grow antlers.

The Eld's deer (Rucervus eldii) is native to areas of Southeast Asia. So named because of their discovery by Lt. Percy Eld in the Manipur Valley of India in 1838, there are three recognized subspecies of R. eldii, which include:

• Rucervus eldii eldii (native to Manipur),
• Rucervus eldii thamin (native to Burma/Myanmar), and
• Rucervus eldii siamensis, (native to Thailand, Annam, and Hainan island).

The Eld’s deer is a large deer that is considered elegant in appearance. They are similar in size to white-tailed deer, but differ somewhat in appearance. Their legs are long and thin, and they have slender bodies with a large head and ears. Their rough coats change color with the season. In summer, they are reddish-brown, and dark brown in winter. Stags often have darker coloring than hinds (females) and have a thick mane of longer hair around the neck.¹

Eld’s deer stags have large bow- or lyre-shaped antlers which sweep backward in a curve of about 40 inches in length, with one smaller tine growing toward the front of the head. Antlers are shed every year and reach their largest size during the breeding season.² Male Eld’s deer grow to about 71 inches in length and weigh from 276 to 386 pounds. They are taller and larger than the hinds, which stand about 60 inches tall.

In their native ranges, Eld’s deer inhabit suitable forest habitats, lowland valleys and plains, avoiding dense forests and coastal areas. This also includes monsoonal forests. Today, they occur in a number of protected areas throughout these areas and have been introduced to numerous countries as game animals, including the United States.²

The diet of Eld’s deer consists largely of grasses, fruits, herbaceous and wetland plants. They are known to graze and to browse opportunistically on cultivated crops such as rice, lentils, maize and peas. On ranches and reserves, Eld’s deer are typically fed a low-protein herbivore diet and alfalfa hay.^1,3

Eld’s deer females can begin reproducing at two years of age and typically continue to do so until they are 10 years of age. They begin estrus in the late winter or early spring and have a long period of ovarian activity (225 to 342 days), during which they average 10 to 17 estrous cycles. After they have mated, the females enter anestrus, which usually occurs in the autumn months.²

Stress, Hypothermia and Hyperthermia in Eld’s Deer

Capturing wild deer is a stressful event which has the potential to cause capture-induced hypothermia or hyperthermia. 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.² It has also been called one of the primary causative factors for the development of capture myopathy.

The specific 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 Eld’s 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 In the case of capture-induced hypothermia, outward signs may also be evident (see below).

Preventing Hypothermia and Hyperthermia in Eld’s Deer

When immobilizing Eld’s deer, the 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 when body temperatures rise to unacceptable levels.

In small animals, hypothermia is more common than in large 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 many deer species. Some drugs used in chemical immobilization may suppress normal thermoregulatory mechanisms, thereby causing 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.^3,4

Monitoring core body temperature is essential in deer sedation and anesthesia,^3,5 and intubation has been widely recommended for any anesthetized Eld’s 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 Eld’s 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.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 deer with capture-induced hyperthermia.

Treating Hypothermia in Eld’s Deer

Hypothermia during anesthetic events is a common adverse effect of sedation or 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 Therefore, having thermal support available in the form of external heating devices during and after anesthesia is prudent. 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 in Eld’s deer 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, 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.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.

To reverse hypothermia water bottles filled with warm water and placed around the deer’s body are very effective. 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.⁴ Returning the animal to a warm environment and/or using heat lamps can also be helpful.