Bloat in Elk During Capture and Chemical Immobilization

Elk (Cervus elaphus), also called wapiti (“white deer” in Shawnee) or red deer, were once found throughout much of the Northern Hemisphere, from Europe through northern Africa, Asia and North America. Extensive hunting and habitat destruction have limited elk to a fraction of their former range, with their populations in eastern North America being dramatically reduced as a result of overhunting. Today, large populations in North America are found only in the western US from Canada through the Eastern Rockies to New Mexico, and in a small region of the northern lower peninsula of Michigan.¹

Elk were reestablished in the eastern US via three transplantations throughout the 20^th-Century. Various elk populations in the western United States, including Yellowstone National Park in Wyoming, contributed to this measure.² In Europe and Asia, elk populations are now confined to protected areas and sparsely-populated regions.

Exceeded in size only by the moose (the largest of the cervids), large male elk average 840 pounds in weight. The largest bulls can exceed 1,100 pounds in weight. The body mass of elk varies considerably within and between populations and increases from south to north. Compared to other large cervids, female elk are more similar to bulls in external appearance and body mass. During winter, males and females have well-developed, dark neck manes that contrast sharply with their brown body color.^2,3

Elk are social animals; in summer, they live in herds with up to 400 individuals. Herds are matriarchal and are typically dominated by a single cow. Elk migrate seasonally and elevationally, with animals being found at higher elevations during summer and lower elevations during winter.

Both males and females are sexually mature at sixteen months, although young males do not mate until they are a few years old and can compete with the larger, more mature males. As the fall mating season approaches, bulls form harems, which they defend with their large size and antlers. In spring, females leave the herds to give birth, while bulls form their own separate herds. After parturition, cows and their calves form nursery groups until calves are ready to join the herd.³

Shortly before the fall rut, in late September and early October, male elk lose the velvet on their antlers and begin to compete for access to females. Dominant males are able to maintain larger harems of females and restrict access to them. Fights between dominant males and intruders can be intense and may result in injury or death.

Female elk protect their calves by hiding them in a secluded area during their first few weeks of life, where they can nurse and protect them during their first year. Male elk do not participate in the care of their young.¹

Elk are browsers who feed on grasses, sedges, and forbs in summer, and woody growth during the winter months. They favor dandelions, aster, hawkweed, violets, clover and mushrooms. Since elk are ruminants, they regurgitate their food and remasticate it to aid in digestion.^1,2

Chemical Immobilization and Bloat Risks in Elk

The management and research of both wild and captive elk often requires chemical immobilization, the favored method of capture over traps, nets and the like. Unfortunately, these animals are prone to a variety of capture‐induced risks while immobilized (via any means), including bloat.⁴ Bloat is a serious condition that is fatal if left untreated. In veterinary medicine, it is frequently seen in large dogs and is known as gastric dilatation-volvulus, or GDV, and can occur spontaneously.

Bloat occurs when an elk’s stomach fills with gas, food, or fluid and subsequently twists. Stomach distension alone is often referred to as dilatation, or “simple bloat”; this can occur spontaneously and can resolve on its own.⁴ Bloat without twisting (GDV) can be life-threatening, but the risk is predicated upon the severity and duration. Bloat has been reported in elk; it has been known to occur spontaneously, but is most closely associated with capture and chemical immobilization events.

In instances of bloat, it is the twisting and flipping of the stomach that precipitates a life-threatening condition. When the stomach becomes severely distended with gas, fluid or food, it puts pressure on the surrounding organs and decreases blood flow to and from these organs. The twisted stomach is more severe, as it completely obstructs blood supply to major organs and can impact blood flow throughout the whole body, resulting in shock.⁴

As an elk’s stomach expands, it exerts pressure on the large abdominal arteries and veins. The blood supply is cut off to the stomach; subsequently, toxic products build up and tissues begin to die. Elk (or any animal experiencing bloat) can go into shock very quickly, and extended periods without treatment increase the risk of further damage and death.^4,5

Each cervid species has its own sedation and anesthesia recommendations, with intra-species variations of dosages due to the diverse individual responses to anesthetic agents.^5,6 These variations are factors in the risk of bloat and other potential complications. Other factors such as stress, venue, individual animal and field conditions must also be taken into account.

Every anesthetic event carries risk, since sedation and anesthesia represent a controlled intoxication of the central nervous system. Since sedatives and anesthetic drugs are never completely devoid of toxicity, the induction of anesthesia invariably carries a risk even to the life of healthy animals.⁴

Drug Classes and Their Effects

Opioids are one of the staple drug classes used in the field immobilization of hoofstock. Unfortunately, opioids can affect thermoregulation, the emetic center (potentially causing nausea and vomiting) and the respiratory system. At a cardiovascular level, bradycardia can occur, as well as arterial hypertension (or hypotension in some cases). Ruminants are thought to be predisposed to gastrointestinal complications (such as bloat) associated with the administration of opioids.⁴

When performing procedures on chemically-immobilized elk, a sternal recumbency position is vital whenever possible, as bloat can more readily occur with animals in lateral recumbency. Other causes of bloat include the use of immobilization drugs such as the α-2-agonists, which can result in a ruminal atony and bloat.⁵

Alpha-2-agonists and opioids used together have a synergistic effect. These drugs inhibit the norepinephrine release by binding with the α-2-adrenoreceptors. Activity in the Sympathetic Nervous System (SNS) is reduced and it results in a decreased heart rate and blood pressure. They induce muscle relaxation, sedation and analgesia, and reduce the stress response. In higher doses, they can induce vomiting because of the activation of the chemoreceptor trigger zone, hypothermia, miosis and hypoxemia. Via inhibition of antidiuretic hormones, an animal usually has an increase of urine production and a decrease of gastrointestinal motility which is thought to result in bloat and colic, mainly in herbivores.⁴

Xylazine was the first α-2-agonist to be used in veterinary medicine. Today, it is used in many species, and is easily available and inexpensive. It promotes good muscle relaxation, sedation and a short period of analgesia. It can, however, cause hyper salivation, muscle tremors in some species and GIT motility suppression. The latter can give rise to ruminal atony and bloat.^4-6

Resolving Bloat in Elk

If an immobilized elk starts to bloat, all administration of immobilizing drugs must be suspended. The animal should be re-positioned into sternal recumbency with the neck extended and the head with the nose pointing down. Intubation of the animal to relieve gases inside may be done; in some cases, trocharization of the rumen is recommended.⁴ If the veterinarian has high confidence that the bloat is being caused by the anesthetic agents, he or she may employ the available reversal agents to antagonize their effect.^4,5

Reversal drugs (e.g., diprenorphine, naltrexone, naloxone) should be given as quickly as possible to avoid the side effects of the immobilizing agents, which may include respiratory depression and cardiovascular issues, among others. Intravenous catheters should be placed and fluid therapy begun, as bloat can cause the heart rate to race at a rate sufficient to cause heart failure.

Medication for shock and electrolytes are all essential in stabilizing the animal. Premature ventricular contraction (PVC) is often associated with bloat. If this arises, intravenous medications will also be needed to stabilize the heart rhythm. If the disturbed heart rhythm is noted early on, the animal’s prognosis for recovery is generally good.¹ In the event of a chemically-immobilized elk’s death, post-mortem gas formation in the alimentary tract should be distinguished from ante-mortem bloating.^5,6