Antelope Bloat During Capture and Chemical Immobilization
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 antelope; it has been known to occur spontaneously, but is most closely associated with capture and chemical immobilization events.
The Mechanism of Bloat
In instances of bloat, it is the twisting and flipping of the stomach that creates 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.1
As the 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. Antelope (or any other animal experiencing bloat) can go into shock very quickly, and extended periods without treatment increase the risk of further damage and death.1,2
Antelope and Chemical Immobilization
The management and research of antelope often requires chemical immobilization. Unfortunately, these animals tend to be prone to a variety of capture‐induced risks while immobilized, including bloat.3 The available literature states that each species of antelope has its own anesthesia recommendations, with intra-species variations of dosages because of diverse individual responses to anesthetic agents.2-4 These variations are factors in the risk of bloat and other potential complications; the attendant factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account.
It should be noted that every anesthetic event carries risk. Anesthesia represents a controlled intoxication of the central nervous system. Since anesthetic drugs are never completely devoid of toxicity, the induction of anesthesia invariably carries a risk even to the life of healthy animals. Finally, the chemical immobilization of free-ranging animals is a form of veterinary anesthesia conducted under the most difficult of circumstances.4
Antelope are ruminants belonging to the families Antilocapridae and Bovidae. The pronghorn antelope, Antilocapra americana, is the only member of the former.Until the advent of potent opiates, the pronghorn was known to be very difficult to safely capture or anesthetize.3 Although carfentanil was reported as effective in many captures, more recently, the combination of butorphanol and azaperone have become popular in the chemical immobilization of pronghorn. 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.1
When performing procedures in chemically-immobilized antelope, 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.1
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 problems, mainly in herbivores.1
It is likely that xylazine was the first α-2-agonist to be used in veterinary medicine. It is used in many species, 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.1-3
Resolving Bloat in Antelope
If an immobilized antelope starts to bloat, all administration of immobilizing drugs should 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.1 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.1,4
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 an animal’s death, post-mortem gas formation in the alimentary tract, especially in ruminants, should be distinguished from ante-mortem bloating, which itself can be a cause of death. In the latter case, there are likely to be signs of asphyxiation.2,4
1Wolfe, 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.
2Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
3Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014,
4Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007, 432 pages.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
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