The word “antelope” is used to describe a wide variety of horned mammals in the Families Bovidae and Antilocapridae. Antelope males (and the females of some species) have unbranched horns that attach to the frontal bones of the skull.Antelope vary widely in size. For example, the royal antelope weighs an average of about four pounds, whereas the eland weighs up to 1,800 pounds.5 Despite being extremely widespread in geography and diverse in size, behavior and habitats, nearly all antelope are considered to be large hoofstock.
Anesthesia is defined as a pharmacologically induced reversible state of amnesia, analgesia, loss of responsiveness, and loss of skeletal muscle reflexes. In contrast, sedation is a drug- induced depression of consciousness during which an animal cannot be easily aroused, but may respond following repeated or painful stimulation. The advantages of sedation over general anesthesia typically focus on patient safety.
The comparative safety of sedation over general anesthesia in human patients is well established. Sedation is associated with decreased risk in other species as well; therefore, sedation is often considered in place of general anesthesia whenever possible.1 Until the advent of potent opiates, the pronghorn antelope (for example) was known to be very difficult to safely capture or anesthetize.4 The focus on the use of sedation in exotic animals such as antelope is a direct result of the perception of greater anesthetic risk in these patients, especially in those that are ill or debilitated.
Other advantages of sedation include general reduction of anxiety and stress related to disease processes such as respiratory disease, and for diagnostic sampling and therapeutics. In some cases, the risk of handling must be weighed against the risk of foregoing diagnostic testing or procedures, or risk of general anesthesia. For these patients, sedation provides an attractive alternative.1
The term “chemical immobilization” covers both anesthesia and sedation. There are many physiological and metabolic changes that occur as a result of chemical immobilization, not all of which are caused by the immobilizing agents. Many of these changes are due to the capture of the animal itself, the most serious of which can bring about a condition called capture myopathy. This is believed to be related to a metabolic acidosis caused by extreme exertion over a short period of time, resulting in necrosis of the large muscle masses of the legs and other areas. This leads to the collapse of the animal and eventual death from acidosis, predation or other factors.3 Since all antelope are prey animals and have evolved with instincts and behaviors gauged to help them survive, this is an inherent risk in antelope capture events of any kind.
Other risks associated with the capture of antelope include aspiration (vomiting), hypothermia, hyperthermia, frostbite, bloat, respiratory depression/arrest and cardiac arrest. Each species of antelope has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.3,4
Disadvantages of sedation can include incomplete elimination of patient movement, patient semi-awareness, and lack of complete analgesia. So, while drugs and lower dosages used for sedation are linked with greater patient safety, they are not entirely without risk. These disadvantages can be overcome with careful dosing and monitoring, effective patient handling and efficient use of analgesics when handing or procedures are expected to produce discomfort.3 The American College of Veterinary Anesthetists (ACVA) has published recommendations for monitoring animals that are sedated without general anesthesia (ACVA recommendations):
In general, sedatives produce calmness, loss of aggression and loss of alertness which are generally required during transportation. In this condition, animals are not immobilized fully and can be aroused by various disturbances. Therefore, they are usually used singly for only very minor procedures, or as adjuncts to dissociative anesthetics for hastening smoother induction and to reduce the quantity of anesthetic for achieving more effective immobilization. The combined synergistic effect of tranquilizers and anesthetic is far greater than the individual effect of either of the two drugs with respect to smooth induction, good muscle relaxation and smoother recovery.3
Sedatives commonly used in veterinary medicine include drugs such as midazolam, alprazolam, amitriptyline, buspirone, clomipramine, dexmedetomidine, diazepam, fluoxetine, lorazepam, paroxetine, sertraline, or trazodone. Acepromazine is also widely used in veterinary medicine as a sedative. It is a member of the phenothiazine class of sedatives and works primarily by blocking dopamine receptors within the brain, thereby depressing certain brain functions.3
Midazolam is often used in human and veterinary medicine for the purposes of pre-anesthesia and sedation and has a wide margin of safety in many species. When combined with an opioid, its effects are synergistic, allowing a reduction of the amount of either drug.4 Dosages most commonly used are 0.5-10 mg/kg, combined with an opioid (butorphanol, buprenorphine, hydromorphone, other). Effects are variable, from slight decrease in activity to lateral recumbency. These effects are likely related to species variability in response and the varying dose rates suggested for different species/groups. In all cases, patients still react somewhat to handling and noxious stimuli.1
When midazolam is used alone, sedation may be adequate in ruminants, camelids and several other species. When used in combination with other drugs (e.g., opioids, ketamine, acepromazine, dexmedetomidine), midazolam provides more reliable sedation. It should be noted that use of sedation and manual restraint alone is inappropriate for any procedure expected to produce discomfort. In mammals, additional sedation can be provided with sub-anesthetic dosages of ketamine, 2-7 mg/kg, or alfaxalone, 1 mg/kg IM. If additional immobilization is essential, low concentrations of inhalant gas can be considered.1
Drugs used for the sedation of antelope will vary, largely depending upon the species at hand, as well as the preference and experience of the veterinarian or wildlife management personnel. The available literature often suggests that dosing higher when in doubt is in fact far safer than dosing conservatively, in that there is more risk to a partially-immobilized animal and to human handlers than there is to a heavily-dosed animal.4,5 This is largely due to the relative safety of modern drug formulations, which allow for much more latitude in dosing without putting an animal’s health or life at risk.