Dehydration in Elk During Capture and Chemical Immobilization

The elk (Cervus elaphus canadensis) is the largest subspecies of red deer (Cervus elaphus) found in North America and in the high mountains of Central Asia. They are a good deal larger than deer, but not as large as a moose, the largest of the cervids. Elk are members of the deer family, (Cervidae, order Artiodactyla). These animals share many physical traits with deer and moose.

Also called wapiti, the North American elk (Cervus elaphus) is further split into six subspecies by some biologists, two of which are now considered extinct:

• Rocky Mountain (Rocky Mountain West) – these elk have the largest antlers of all subspecies
• Roosevelt’s (Coastal Pacific Northwest) – these are the largest in body size of all subspecies
• Tule (Central California) – these have the smallest body size of all subspecies
• Manitoban (northern Great Plains)
• Merriam’s (Southwest and Mexico) – Extinct
• Eastern (east of the Mississippi) – Extinct^1,2

Elk range in color from a light brown in winter to a dark tan in summer and have buff-colored rumps. In winter, they grow a dark brown, shaggy mane hangs from the neck to the chest. Bull elk (males) have large, spreading antlers. Like other members of the deer family, the antlers of bull elk grow during spring and summer beneath a covering known as velvet. In late summer, the velvet dries and falls off to reveal fully-grown antlers. These are shed in early spring, with new antler growth beginning soon afterward.

Adult bull elk typically weigh 600 to 800 pounds, with adult cows weighing 400 to 500 pounds. They have thick bodies, short tails, long legs, and stand from 4.5 to 5 feet high at the shoulder.

Elk are found throughout the western areas of North America. In the Pacific Northwest of the US, there are two subspecies that occupy the opposite sides of the Cascade Crest. Roosevelt elk (Cervus canadensis roosevelti) are found in the coastal ranges of the Olympic Peninsula, southwestern Washington, and the western slopes of the Cascade Range. Rocky Mountain elk (Cervus canadensis nelsoni) are found in the mountain ranges and steppes of eastern Washington; many of these had their origins in populations that were transplanted from Yellowstone National Park in the early 1900s.¹Rocky Mountain elk are slightly smaller and lighter in color than Roosevelt elk, the antlers of Rocky Mountain elk are also smaller and with longer tines.²

Due to their body size and herding behavior, elk require large amounts of food. In spring and summer when food is plentiful, elk are primarily grazers, eating grasses, sedges, and a variety of flowering plants. In fall, they become browsers, feeding on sprouts and branches. During late fall and winter, they continue to eat grasses when these are available and not covered by snow. Like other cervids, elk are ruminants.

Elk and Chemical Immobilization

The field immobilization of elk may be required for medical examination, blood sample collection, and animal identification, and the importance of performing such procedures for research and conservation projects is widely acknowledged.³ As these activities continue to become more common, the need to assess their negative effects increases in order to ensure ethical standards and the validity of research results. Research in this area has revealed that the physiological and behavioral effects of capture are as important as the direct risks of injury or death of an animal.²

There are a number of common stressors relating to the chemical immobilization of elk that can lead to complications during or after an immobilization (sedation or anesthetic) event. The overall health of an individual animal is also a factor affecting the potential for complications during and after anesthesia.

These stressors fall into four categories:

• Physiological: Heavy exercise, hemorrhage, hyperthermia, shock, pain, infection
• Physical: Trauma/surgery, intense heat/cold
• Chemical: Hypoxemia, acid-base imbalance, anesthetic drugs
• Emotional: Anxiety, fear³

Chemical immobilization agents are represented by the third category, although elements of the other three are often included in immobilization events. The physical stress of capture and/or attempts to escape during capture on the part of an animal certainly constitute physiological stress; surgical and even environmental conditions can bring about physical stress, and anxiety and fear are nearly always a component to some degree in a capture scenario.

The effects of acute stress during capture can include spikes in adrenaline, cortisol levels, heart rate, blood pressure, respiration, metabolic rate, blood glucose, lactic acid and body temperature, while bringing about a decrease in pH and a redistribution of blood within the organs. The effects of capture and anesthesia can activate the fight-or-flight response, HPA-axis activation, hyperthermia, respiratory depression (hypoxemia), lactid acid build-up, acidosis; in severe cases, this can lead to neurological/myocardial dysfunction, multi-organ failure, capture myopathy and death.⁴

Dehydration Risks in Elk

Initially, dehydration may seem like a minor concern compared to some surgical complications, but inasmuch as it can lead directly to cardiac arrest, dehydration (a reduction of the body’s water content) is potentially quite dangerous. All animals require water to ensure their bodies are working properly. It is so important that essentially all bodily functions require it to remain operative. If an animal loses more water and electrolytes than it is taking in, it will begin to dehydrate and its health will quickly deteriorate.

Electrolytes are minerals that are carried in the fluids of the body. They naturally occur in all animals, and are essential for proper health. Electrolytes are comprised of sodium, chloride, and potassium, and facilitate the movement of nutrients into cells, aid in muscle function, and help regulate nerve activities.^3,4 An elk’s natural activities—breathing, urinating, defecating and simple evaporation—all cause it to lose fluids. When an animal eats and drinks, the lost water and electrolytes are replaced. If the animal’s fluid intake becomes less than what they are losing, dehydration will occur. This causes a reduction in bodily fluids that reduces blood flow and the delivery of oxygen to organs and tissues.

Understanding Dehydration in Elk

To understand dehydration, one must first understand the distribution of fluid and water in the body. Total body water (TBW) comprises approximately 60% of an animal’s body weight. Approximately 67% of TBW is found inside the body’s cells; this is referred to as intracellular fluid (ICF). The remaining 33% of TBW is the extracellular fluid (ECF), which comprises:

• Interstitial fluid, which bathes cells and tissues (~24% of TBW)
• Plasma, the liquid portion of blood, which constitutes most of intravascular volume (~8%–10% of TBW)
• Transcellular fluid, which comprises synovial joint fluid, cerebrospinal fluid, bile, and the fluid in the linings of the peritoneal cavity, pericardium, and pleural space (~2% of TBW)³

A formula for the distribution of fluids in the body is the 60:40:20 rule: 60% of an animal’s body weight is water, 40% of body weight is ICF, and 20% of body weight is ECF.^3,4

Dehydration can be caused by hyperthermia, chronic vomiting or diarrhea, excessive urination or wound drainage. Due to the stressful nature of capture and chemical immobilization events, they have been known to bring about dehydration. In both human and veterinary practices, IV fluids are usually administered prophylactically, depending on the nature of the procedure. Veterinarians often provide fluid therapy to patients for correction of dehydration, expansion and support of intravascular volume, correction of electrolyte disturbances, and encouragement of appropriate redistribution of fluids that may be in the wrong compartment (e.g., peritoneal effusion).³

The available literature states that each species of cervid has its own anesthesia recommendation with intra-species variations of dosages because of individual responses to anesthetic agents.^3,4 These variations are factors for the risk of dehydration in these species, and related factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account. Prior to the advent of some of the newer drug formulations, some hoofstock species were known to be notoriously difficult to immobilize successfully.

Treating Dehydration in Elk

Monitoring core body temperature is essential in elk anesthesia.⁴ During anesthetic/immobilization events, hydration status can be assessed using various tests. One of the easiest to perform is a skin tent test to check the turgor (moisture level) of the skin. To do this, the skin over the thorax or lumbar region is pulled away from the back. In a well-hydrated animal, the skin immediately returns to its normal resting position. If the tent formed remains standing, it is a likely indication of dehydration.

If there is evidence of dehydration in an elk during a procedure, all administration of immobilizing drugs must be immediately suspended. Fluid therapy should begin in the form of lactated Ringer’s solution or 0.9% saline, IV, SQ or IP.⁵

Perioperative IV fluid therapy is very common in veterinary medicine and allows practitioners to restore intravascular volume, correct dehydration and administer IV medications quickly.⁴ While perioperative fluid therapy under many field conditions may be impractical, fluids should always be available in the case of dehydration when chemically immobilizing elk.