Dehydration in Impala During Capture and Chemical Immobilization
The impala (Aepyceros melampus) is the most common antelope of the savannas of eastern and southern Africa and the bushveld regions of South Africa. Known for its agility and spectacular leaps when startled or evading predators, it is a member of the family Bovidae, and the only member of the subfamily (or tribe) Aepycerotini.1 The impala is medium-sized as compared to larger antelopes like the kudu and sable. It has slender, well-developed legs and a long neck. Impala males boast wide, lyre-shaped horns that are 18–36 inches or longer.2
Impala have a tan coat of varying shades, with males and females being similarly colored. They also have a reddish-brown saddle and white markings at the eyes, the inside of the ears, throat, the underside of the torso and tail. There are black markings at the ears, tail and back feet. There is a less common subspecies in southwest Africa called the black-faced impala (Aepyceros melampus petersi), which is darker in color.1
Impala both graze and browse for food. When grazing, they consume grass, and when browsing, they feed upon a wide variety of vegetation, including fruits, seedpods, shoots as well as leaves of trees and bushes.3
Impala are both diurnal and nocturnal. Typically, they are most active immediately after sunrise and just before sunset. Female impalas and their offspring occupy herds which number from 15 to 100 individuals.3 During the wet season, females become highly territorial and defend the home ranges. Young males form non-territorial bachelor herds of up to 30 individuals. During the dry season, male and female herds mix together.
Unlike many of the well-known African antelopes, impala have a polygynous mating system, with each male mating with a number of females,2 and their breeding activity spans from March through May. During this time, pregnant females live in isolation until they give birth. After 190 to 200 days, a single calf is born, after which the calf and the mother rejoin the herd.3
Chemical Immobilization, Stressors and Complications
The field immobilization of impala is sometimes required for medical examination, blood sample collection, and animal identification, and the importance of these activities for research and conservation projects is well-established.4 Chemical immobilization is also routinely necessary in the zoo setting. Research in this area has revealed that the physiological and behavioral effects of capture are as important as the direct risks of injury or death of an animal during chemical immobilization events.5
There are a number of common stressors related to the chemical immobilization of impala and other antelope that can lead to complications during or after an anesthetic event. The overall health of an individual animal (which might be poor, and in some cases the very reason for its capture) is also a factor affecting the potential for complications during and after anesthesia.
In general, these stressors fall into four categories:
- Physiological: Heavy exercise, hemorrhage, hyperthermia, shock, pain, infection
- Physical: Trauma/surgery, intense heat/cold
- Chemical: Hypoxemia, acid-base imbalance, anesthetic drugs
- Emotional: Anxiety, fear6
The agents used in chemical immobilization are represented by the third category, although elements of the other three can be present during immobilization events. The physical stress of capture constitutes physiological stress, surgical and even environmental conditions can bring about physical stress, and anxiety and fear are nearly always a component to the capture scenario.
Stress during capture can include spikes in adrenaline, cortisol levels, heart rate, blood pressure, respiration, metabolic rate, blood glucose, lactic acid and body temperature, while bringing about a decrease in pH and a redistribution of blood within the organs.6,7 The effects of capture can activate the fight-or-flight response, hyperthermia, respiratory depression (hypoxemia), HPA-axis activation, lactic acid build-up and acidosis. In some cases, this can lead to neurological/myocardial dysfunction, multi-organ failure, capture myopathy and death.7
Dehydration in Impala
Dehydration (a reduction of the body’s water content) may seem like a relatively minor concern compared to some of the more serious surgical complications that can arise during chemical immobilization events. In truth, since it can lead directly to cardiac arrest, dehydration is potentially quite dangerous. All animals require water to ensure that their bodily functions remain operative, and if an animal loses more water and electrolytes than it is taking in, it will begin to dehydrate and its health will quickly deteriorate.
Electrolytes are minerals that naturally occur in all animals, and they are essential for maintaining proper health. They are comprised of sodium, chloride, and potassium, and facilitate the movement of nutrients into cells, aid in muscle function, and help regulate nerve function.6,7 An animal’s natural activities—including breathing—can cause it to lose fluids. In general, when an animal eats and drinks, the lost water and electrolytes are replaced. If its fluid intake is less than what it is losing, dehydration will occur. This causes a reduction in bodily fluids that reduces blood flow and the delivery of oxygen to organs and tissues.
The Mechanics of Dehydration
An understanding of the distribution of fluid and water in the body is necessary in understanding dehydration. Approximately 60% of an animal’s body weight is comprised of total body water (TBW). Nearly 70% of TBW is found inside the body’s cells, which is known as intracellular fluid (ICF). The remaining 33% of TBW is the extracellular fluid (ECF), which is made up of:
- Interstitial fluid, which bathes cells and tissues (~24% of TBW)
- Plasma, the liquid portion of blood, which constitutes most of intravascular volume (~8%–10% of TBW)
- Transcellular fluid, which comprises synovial joint fluid, cerebrospinal fluid, bile, and the fluid in the linings of the peritoneal cavity, pericardium, and pleural space (~2% of TBW)5
An approximate formula for the distribution of fluids in the body is known as the 60:40:20 rule:
- 60% of an animal’s body weight is water,
- 40% of body weight is ICF, and
- 20% of body weight is ECF.5,6
Dehydration can be brought on by hyperthermia, chronic vomiting or diarrhea, excessive urination or wound drainage. Due to the stressors connected with capture and chemical immobilization events, these have also been known to bring about dehydration. In both human and veterinary medicine, IV fluids are usually administered prophylactically, depending on the nature of the procedure. Veterinarians often provide fluid therapy to their patients for many reasons, including correction of dehydration, expansion and support of intravascular volume, correction of electrolyte disturbances, and encouragement of appropriate redistribution of fluids.5
The available literature maintains that different species of antelope have different anesthesia recommendations because of the diverse individual responses to anesthetic agents across species.5,6 These variations represent risk factors for dehydration in all antelope species. Other factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account. Prior to the development of newer drug formulations, some antelope species were known to be notoriously difficult to immobilize successfully.
Treating Dehydration in Impala
In all antelope anesthesia, monitoring core body temperature is considered essential.6 Intubation has also been widely recommended for any anesthetized antelope that needs to be transported or anesthetized for greater than one hour. During anesthetic events, hydration status can be assessed using various tests, the easiest being a skin “tent test” to check the turgor (moisture level) of the skin. To do this, the skin over the thorax or lumbar region is pulled away from the back. In a well-hydrated animal, the skin immediately snaps back to its normal resting position. If the tent formed remains standing, it is an indication of dehydration.
If there is evidence of dehydration in an antelope during a procedure, all administration of immobilizing drugs must be immediately suspended. Fluid therapy should begin in the form of lactated Ringer’s solution or 0.9% saline, IV, SQ or IP.6
Perioperative IV fluid therapy is often recommended in veterinary medicine; this allows practitioners to restore intravascular volume, correct dehydration, and administer IV medications quickly.7 While perioperative fluid therapy under many field conditions may be impractical, fluids should always be available in the case of dehydration when chemically immobilizing impala.
4Laricchiuta P, De Monte V, Campolo M, Grano F, Iarussi F, Crovace A, Staffieri F. Evaluation of a butorphanol, detomidine, and midazolam combination for immobilization of captive Nile lechwe antelopes (Kobus magaceros). J Wildl Dis. 2012 Jul;48(3):739-46.
5Brivio F, Grignolio S, Sica N, Cerise S, Bassano B (2015) Assessing the Impact of Capture on Wild Animals: The Case Study of Chemical Immobilisation on Alpine Ibex. PLoS ONE 10(6): e0130957.
6Kreeger T., Arnemo, J., Raath, J. Handbook of Wildlife Chemical Immobilization, International Edition, Wildlife Pharmaceuticals, Inc., Fort Collins, CO. (2002).
7Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014,
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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