In North America, 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, a group of animals also known as cervids. Deer live on almost every continent on the globe; there are around a half dozen species that are common in North America, as well as other subspecies and non-native species.1
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. While the antlers grow, they are covered by a thin layer of downy skin known as velvet. When the antlers are fully grown, the velvet dries and is typically rubbed off by the animal.2 Antlers serve as ornamentation for breeding purposes, as well as weapons during the mating season.
Most deer prefer forested areas where they can find plenty of vegetation for eating and hiding, but they readily adapt to other environments. Deer are primarily herbivores that browse for roots, twigs, bark, grass, leaves, and other vegetation. They are also partial to fruits, vegetables, and flowers, as many suburban gardeners are aware. Deer have a four-chambered stomach, and are cud-chewing herbivores (ruminants).1
There are an estimated 35 million deer in the U.S., with the white-tailed deer (or whitetail deer, Odocoileus virginianus)being the most common. These deer weigh from 150-300 pounds, and stand from 37-87 inches at the shoulder. White-tailed deer are primarily distributed east of the Rocky Mountains and in most of Mexico, although in recent years, they have expanded farther west in the United States and into western Canada.
Also called the Virginian deer, whitetails get their name from the white underside of their tail. Upon seeing predators, they raise their tail and flash the white underside to let the predator know it has been seen, thus reducing the possibility of an actual attack. The whitetail’s coat changes from a reddish-brown for the spring and summer to a gray-brown in the winter.
Capturing wild deer 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 white-tailed 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).
When immobilizing 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.
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 deer due to excitement and struggling while darting.1-4
Monitoring core body temperature is essential in deer anesthesia,3,5 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
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.
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:
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.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 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.4 Returning the animal to a warm environment (if possible) and/or using heat lamps (if available) can also be helpful.
1safariclub.org.