Bloat in Eld’s Deer During Capture and Chemical Immobilization

The Eld's deer (Rucervus eldii) is a deer species that is indigenous to areas of Southeast Asia. So named because of their discovery by Lt. Percy Eld in the Manipur Valley of India in 1838, there are three recognized subspecies of R. eldii. These include:

• Rucervus eldii eldii (also called the Sangai, it is native to Manipur),
• Rucervus eldii thamin (also called the Thamin, it is native to Burma/Myanmar), and
• Rucervus eldii siamensis, (also called the Siamese Eld’s deer, it is native to Thailand, Annam, and Hainan island).

A large deer that is considered regal in appearance, Eld’s deer are similar in size to white-tailed deer, but differ somewhat in appearance. Their legs are long and thin, and they have slender bodies with a large head and ears. Their rough coats change color with the season. In summer, they are reddish-brown, and dark brown in winter. Stags often have darker coloring than hinds (females) and have a thick mane of long hair around the neck.¹

Eld’s deer stags have very large bow- or lyre-shaped antlers which sweep back in a curve of about 40 inches in length. One smaller tine grows toward the front of the head. Antlers are shed every year and reach their largest size during the breeding season.² Stags grow to about 71 inches in length and weigh from 276 to 386 pounds. They are taller and larger than the hinds, which stand about 60 inches tall.

In their native ranges, Eld’s deer inhabit forested areas, lowland valleys and plains, avoiding dense forests and coastal areas. Today, they occur in a number of protected areas throughout these areas and have been introduced to numerous countries as game animals, including the United States.²

The Eld’s deer’s diet consists largely of grasses, fruits, herbaceous and wetland plants. They are known to graze and to browse opportunistically on cultivated crops such as rice, lentils, maize and peas. On ranches and reserves, Eld’s deer are typically fed a low-protein herbivore diet and alfalfa hay.^1,3

Eld’s deer females can begin reproducing at two years of age and typically continue to do so until they are 10 years of age. They begin estrus in the late winter or early spring and have a long period of ovarian activity (225 to 342 days), during which they average 10 to 17 estrous cycles. After they have mated, the females enter anestrus, which usually occurs in the autumn months.²

Chemical Immobilization and Bloat Risks in Eld’s Deer

The management and research of Eld’s deer often requires the use of chemical immobilization. Unfortunately, these animals tend to be prone to a variety of capture‐induced risks while immobilized, including bloat.⁴ This is a serious condition that is usually 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 Dangers of Bloat in Eld’s Deer

Opioids are one of the chief 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 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. 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. Through the 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.^4,5

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 Eld’s Deer

If an immobilized animal begins to show signs of 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 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.

To stabilize the animal, medication for shock and electrolytes are essential. Premature ventricular contraction (PVC) is often associated with bloat. If this arises, intravenous medications will also be needed to stabilize the heart rhythm. If a disturbed heart rhythm is noted early on, the animal’s prognosis for recovery is generally good.⁴ In the event of a chemically-immobilized 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