Bloat in Barasingha Deer During Capture and Chemical Immobilization

Like other deer species, the barasingha deer (Rucervus duvaucelii) belongs to the order Artiodactyla, which include hoofed mammals with an even number of toes on each foot. Deer also belong to the family Cervidae, and are commonly referenced as cervids. The barasingha deer is one of the most widely-recognized deer of the Indian subcontinent. Also called the swamp deer, it is typically found in marshy, damp areas.

The barasingha deer is a large, long-legged deer, with a short head and long, broad ears. Larger stags may have an overall length of up to 71 inches (180 cm) and weigh up to 620 lbs (280 kg). Their coats are a yellowish-brown color, which darkens during the winter months. Some individuals have yellowish spots scattered over their coats. The hair around the deer’s neck may be longer, forming a shaggy mane.¹

The barasingha deer is extinct in both Bangladesh and Pakistan, where it once roamed freely. Today, there are fragmented populations in central and northern India, as well as southwestern Nepal.^1-3 The name “barasingha” is loosely derived from the Hindi words for “twelve ends”, referencing this deer’s antlers, which can have from 12 to 20 tines in mature stags. Barasingha deer have a lifespan of up to 20 years.²

In their native range, barasingha deer have several natural predators, including the tiger. As a result, they have developed an apprehensive, nervous manner and are always on high alert. They have a loud, barking call that they use to signal danger that is said to be similar to the alarm call of the roe deer. Barasingha deer feed by day, but can also be found resting during the hottest times of the day. In the winter, large herds form, which dissipate during the summer into smaller herds composed of females and their fawns. During the summer, males live separately from females in small bachelor groups.^2,3

Female barasingha deer are monoestrous, and usually have a single fawn after eight months of gestation. Fawns are weaned at around six months, and the female is ready to breed again about a year after giving birth. Stags reach puberty at two years of age, and females reach puberty at 18 to 24 months.¹

In the late 1960s, the numbers of barasingha deer in India and Nepal dropped drastically due to hunting, habitat loss and disease. It was brought back from the verge of extinction over several decades through successful breeding programs and conservation practices. Habitat improvement and captive breeding led to a substantial increase in the population.⁴ Today, their populations are no longer in danger, and the barasingha deer has been introduced to many areas, including the United States, where they may be hunted on ranches and reserves.

Bloat Risks in Barasingha Deer

The management and research of barasingha deer often requires chemical immobilization. Unfortunately, these animals tend to be prone to a variety of capture‐induced risks while 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 occurs when an animal's stomach fills with gas, food, or fluid and subsequently twists. Stomach distension alone is often referred to as dilatation, or “simple bloat” that can occur spontaneously and can resolve on its own.¹ Bloat 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 Dynamics of Bloat

When bloat occurs, it is the twisting and flipping of the stomach that brings about a life-threatening condition. When an animal’s 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. 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 deer species 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

Drugs Used for Chemical Immobilization

Opioids are one of the main drug classes used in the field immobilization of barasingha deer, and they have been a staple for the immobilization of wild hoofstock since the 1960s. 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) when opioids are used.⁴

When performing procedures on chemically-immobilized 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 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. Such combinations 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 Barasingha Deer

In the event that an immobilized barasingha 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 to relieve gases 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.^5,6

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 initiated, since bloat can cause the heart 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.⁴ In the event of a chemically-immobilized animal’s death, post-mortem gas formation in the alimentary tract should be distinguished from ante-mortem bloating, which can be a cause of death in itself.^5,6

¹worlddeer.org.
²animalia.bio.
³animaldiversity.org.
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.