The elk (Cervus elaphus canadensis) is the largest subspecies of red deer (Cervus elaphus) found in North America and in high mountains of Central Asia. It is a member of the deer family (Cervidae, order Artiodactyla). Genetic studies suggest that what is considered the “red deer” by biologists may in fact be three species: the European red deer, the Tibetan–West Chinese red deer, and the elk—but this assessment remains controversial.1
Also called wapiti in North America, elk were once found throughout much of the Northern Hemisphere, from Europe through northern Africa, Asia and North America. It is believed that extensive hunting and habitat destruction have limited them to a portion of their former range.2 Today, large populations in North America are found only in the western United States from Canada through the Eastern Rockies to New Mexico, and in a small region of the northern lower peninsula of Michigan.
Exceeded in size only by the moose (the largest of the cervids), adult male elk average around 840 pounds, while the largest bulls can exceed 1,100 pounds in weight. Compared to other cervids, female elk are more similar to the males in external appearance and body mass. Elk range in color from dark brown in winter to tan in summer and have a characteristic lighter-colored rump. During winter, males and females have well-developed, dark neck manes. Elk have a long head with large ears; males have branching antlers as long as 36 to 60 inches from tip-to-tip.
Elk are browsers who feed on grasses, sedges, and forbs. They especially favor dandelions, aster, hawkweed, violets, clover and mushrooms. The elk’s diet varies seasonally. Spring forage includes early -greening grasses and forbs that are highly palatable, succulent and nutritionally rich. During summer, the elk’s diet is composed of 60% to 100% forbs (dandelion, geranium, asters, clovers). Fall begins a period when leafy vegetation contains reduced protein but is still a good source of energy. Grass averages 73% of the fall diet and elk begin to eat more shrubs. In winter, grasses may make up as much as 84% of an elk’s diet.1 Elk are ruminants, regurgitating their food and remasticating it to aid in digestion.1,2
Elk males and females are considered sexually mature at sixteen months, although young males do not usually mate until they are a few years old and can compete with larger, more mature males. Gestation generally lasts between 240 and 262 days and results in a single birth. Shortly before the fall rut (late September and early October), male elk lose the velvet on their antlers and begin to compete for access to females. Fights between dominant males and intruders can be intense and result in injury, exhaustion, or death.
Elk are highly social animals and often live in herds with as many as 400 individuals. Herds are matriarchal and are typically dominated by a single cow. These herds will migrate elevationally, occupying higher elevations during the summer and lower elevations during winter. As the fall mating season approaches, bulls form harems. In the spring, the sexes separate with females leaving to give birth, while bulls form their own separate summer herds.
Capturing wild elk 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 elk is 104°F (40°C), with 107°F (44°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).
The constant monitoring of body temperature is essential when immobilizing elk. 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 elk. Some of the 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 elk due to excitement and struggling while darting.1-4
Monitoring core body temperature is essential in elk anesthesia,3,5 and intubation has been widely recommended for any anesthetized elk 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 elk anesthesia in wildlife and captive care.3
Given that capture-induced hyperthermia in some elk may be severe, one method recommended for improving their chances for survival is to physically cool captured animals. Recommendations for cooling captured elk 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 elk 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 elk’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.