Axis Deer Sedation

Native to the Indian subcontinent, the Axis deer (Axis axis) can be distinguished from many other deer species by the white spots on its coat. These give it a similar appearance to juvenile white-tailed deer, although adult Axis deer are only slightly smaller than adult white-tailed deer. Axis deer have been introduced into parts of Hawaii, Texas, California, Mississipi, Alabama, and several countries outside of the United States. While they were originally intended to remain captive, many escaped captivity and established wild populations.

Axis deer can reproduce very quickly, which gives them an advantage over local deer populations. Today, it is considered an invasive species in some of the areas in which it has been introduced because it is an effective competitor for resources.¹ Some invasive species such as Axis deer were introduced to certain areas as game animals; in their new environments, they have fewer predators and more resources in their non-native environments, and can easily outcompete local species. For example, in the Hawaiian islands, the Axis deer population is reportedly growing at between 20% to 30% each year.²

Axis deer are very social, and are usually found in herds ranging from a few animals to more than 100 individuals. The leaders of herds are usually mature, experienced does. Unlike native North American deer, adult male axis deer are normally found living with herds of young and old animals of both sexes. Like elk, rutting male Axis deer emit bugle-like bellows, and both sexes can produce alarm calls.²

In the wild, mature Axis deer bucks in rutting condition may be found throughout the year, with each buck having an independent reproductive cycle which may not be synchronized with that of other bucks in the herd.^2,3 Females experience estrous cycles throughout the year, with each cycle lasting approximately 3 weeks. Pregnant females may be found year-round, but most breeding lasts from mid-May through August.

Anesthesia vs. Sedation in Axis Deer

The sedation of Axis deer is often required for the purposes of research, wildlife management and medical care. First, it will be necessary to distinguish between sedation and anesthesia. While the terms “sedation” and “anesthesia” are often used interchangeably, these are two different methods of chemical immobilization.

• Anesthesia is a pharmacologically-induced reversible state of amnesia, analgesia, loss of responsiveness, and loss of skeletal muscle reflexes.
• 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 relative safety of sedation over general anesthesia in both animal and human patients is well-established, therefore, sedation is often considered in place of general anesthesia whenever possible.⁴ Until the advent of potent opiates, some deer species were known to be very difficult to safely capture or immobilize chemically.⁵ The focus on the use of sedation in exotic animals such as Axis deer 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 a 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 the risk of general anesthesia.⁴

Risks Associated With Chemical Immobilization

Various physiological and metabolic changes occur in an animal’s body 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 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.^4-6 Since all deer are prey animals and have evolved with instincts and behaviors gauged to help them survive, this is an inherent risk in any capture of deer.

Additional risks that are associated with the chemical immobilization of Axis deer include vomiting and aspiration, hypothermia, hyperthermia, frostbite, bloat, respiratory depression/arrest and cardiac arrest. Each species of deer has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.^4,5

Disadvantages of sedation can include incomplete elimination of an animal’s movement, 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.⁴ The American College of Veterinary Anesthetists (ACVA) has published recommendations for monitoring animals that are sedated without general anesthesia (ACVA recommendations):

• Palpation of pulse rate, rhythm and quality
• Observation of mucous membrane color and CRT
• Observation of respiratory rate and pattern
• Auscultation
• Pulse oximetry, supplemental oxygen, endotracheal tube (where applicable) and materials to obtain vascular access should be readily available⁴

Agents for the Sedation of Axis Deer

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 sedatives and anesthetics is far greater than the individual effect of either of the two drugs with respect to smooth induction, good muscle relaxation and smoother recovery.⁴

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.⁴

Midazolam is often used for the purposes of sedation and pre-anesthesia 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.⁵ 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. In all cases, patients still react somewhat to handling and certain stimuli.⁶

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.^4,7

The drugs used for sedating Axis deer will vary depending upon the species, as well as the preference and experience of the veterinarian or wildlife management personnel. The literature suggests that dosing higher when in doubt is in fact 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 deer.^6-8 This is largely due to the relative safety of modern drug formulations, which allow for much more latitude in dosing without putting the animal’s health or life at risk.