Bloat in Axis Deer During Capture and Chemical Immobilization

The axis deer (Axis axis)—also known as the spotted deer or chital deer—is a deer species that is native to the Indian subcontinent. It is a moderately large, spotted deer that was introduced into Texas and other parts of the U.S. in the early 1900s. These deer prefer sparse, secondary forests that supply adequate drinking water and shade, and they tend to avoid rugged terrain.^1,2

Axis deer are social animals, congregating in herds can comprise from 6 to 30 individuals, with two or three stags. Adult females and their fawns from the current and previous year form matriarchal herds. Male Axis deer typically live in a hierarchy with larger and older males dominating smaller and younger ones.² The period of the Axis deer’s highest activity is morning and late afternoon. During the heat of the day, they can be found resting in the shade. When the weather is hot, they tend to remain near water, drinking in the mornings and evenings.²

Axis deer are always on the alert in anticipation of predators. They are vocal animals and are known to emit bellows and alarm barks. Males may moan during aggressive displays; females and juveniles may bark persistently when alarmed.³

The Axis deer is herbivorous, with a highly generalized diet of grasses and vegetation. Males grow antlers on a yearly basis, which they use to compete with other males for mating access to females. Unlike other deer, Axis deer usually form mating pairs instead of engaging in polygyny. Females can reproduce multiple times each year, and the offspring are likely to make it to adulthood—meaning that populations can grow very quickly. This can give rise to management problems in areas where these deer have been introduced.

Like all deer, axis deer are cervids (family Cervidae). Deer are native to all continents except Australia and Antarctica, although many species have been widely introduced outside of their original habitats as game animals. In all save one species of deer, only the males carry antlers; in the reindeer or caribou (Rangifer tarandus), both sexes have antlers.³

Chemical Immobilization and Bloat Risks in Axis Deer

The management and research of Axis deer sometimes requires their capture, the preferred method of which is chemical immobilization. Unfortunately, these animals tend to be prone to a variety of capture‐induced risks while chemically-immobilized, 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 is described as an animal's stomach filling with gas, food, or fluid and subsequently twisting. Stomach distension alone is often referred to as dilatation, or “simple bloat” which can occur spontaneously and can resolve on its own.^4,5Bloat without twisting (GDV) can be life threatening, but the risk is predicated upon the severity and duration. Bloat is a condition that has been reported in many species of deer; it has been known to occur spontaneously, but is most closely associated with capture and chemical immobilization events.

The Mechanism of Bloat in Axis Deer

In instances of bloat, it is the twisting and flipping of the stomach that presents life-threatening circumstances. 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 a deer’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. Axis deer (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 species of deer has its own 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

Immobilizing Drugs and Procedures

One of the staple drug classes used in the field immobilization of hoofstock is the opioids. Opioids can affect thermoregulation, the emetic center (potentially causing nausea and vomiting), and the respiratory system. Bradycardia can occur with the use of opioids, 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.⁵

When performing procedures on chemically-immobilized Axis deer, 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 subsequently, bloat.⁴

Alpha-2-agonists (α-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

The first α-2-agonist to be used in veterinary medicine was xylazine. 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 Axis Deer

If an immobilized Axis deer 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.⁴If 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 agents (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 will be 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.⁴ In the event of a chemically-immobilized Axis deer’s death, post-mortem gas formation in the alimentary tract should be distinguished from ante-mortem bloating, which itself can be a cause of death.^5,6

¹J. Schmidly, J., Bradley, R. The Mammals of Texas, Seventh Edition 1994, University of Texas Press.
²tsusinvasives.org.
³animalia.bio.
⁴Wolfe, B. (2015). Bovidae (except sheep and goats) and antilocapridae. In Miller, R. E., Fowler, M. E. (eds) Zoo and Wild Animal Medicine. (Volume 8). St Louis, Missouri: Elsevier Saunders, 626-644.
⁵Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
⁶Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007, 432 pages.