The kudu is one of the largest African antelopes. There are two subspecies: the greater kudu (Tragelaphus strepsiceros),and the lesser kudu (Tragelaphus imberbis). The former is second in size to the eland, Africa’s largest antelope. The greater kudu inhabits the dense brush and forested areas of southern Africa, while the lesser kudu is found in the arid lowland thornbush of northeast and East Africa.1 These antelope forage on a wide variety of trees, shrubs, vines, herbs, seedpods, fruits and grasses. Both species prefer the green growth along watercourses in dry seasons and disperse through deciduous woodlands during rainy seasons.2
Since the integration of veterinary medicine into wildlife management programs, zoological collections, exotic animal ranching expansions and the private collection of wildlife species, the veterinary care of kudu has become commonplace.1As a result, wildlife managers and veterinarians are frequently called upon to anesthetize and handle these animals. Since both species of kudu are forest-dwellers and elusive, difficulties in capturing them can increase the risks for a variety of complications during capture/chemical immobilization.
Bloat is a serious condition that can be fatal if left untreated. In veterinary medicine, it is frequently seen in large dogs and is known as gastric dilatation-volvulus (GDV), and it 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.3 Bloat without twisting (GDV) can be life-threatening, but the risk depends upon the severity and duration. Bloat is a condition that has been reported in many species of antelope; though it has been known to occur spontaneously, it is most closely associated with capture and chemical immobilization events.
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 completely obstructs blood supply to major organs and can impact blood flow throughout the whole body, resulting in shock.3
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.3,4
The management and research of kudu often requires chemical immobilization. Unfortunately, antelope in general are prone to a variety of capture‐induced risks while immobilized, including bloat.5 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.4,5 These variations are factors in the risk of bloat and other potential complications. 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. Although carfentanil was long reported to be effective in many captures, more recently, the combination of butorphanol and azaperone have become popular in the chemical immobilization of antelope. Opioids can affect thermoregulation, the emetic center (potentially causing nausea and vomiting), and the respiratory system. Ruminants are also thought to be predisposed to gastrointestinal complications (such as bloat) associated with the administration of opioids.3
When performing procedures in any 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.3
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.3
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.3-5
If an immobilized antelope starts to bloat, all immobilizing drugs should be immediately withdrawn. 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, they may employ the available reversal agents to antagonize their effect.3,6
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.3
1awf.org.