Over 60 species of deer are recognized worldwide, and deer occur on all continents except Antarctica. Deer are hoofed mammals which belong to the order Artiodactyla, and to the family Cervidae; thus, these animals are also known as cervids. Deer occupy a range of diverse habitats, from rainforests to temperate zones. There are seven species of deer that are native to North America, with many sub-species. These range from Canada all the way through Central America and from the east coast to the west coast.1 Cervids differ from other ruminants in that males grow antlers that are comprised of bone. These are shed and regrown annually, and increase each year in size and intricacy.
The Axis deer (Axis axis) can be distinguished from many other deer species by the white spots on its coat. Although the axis deer is native to the Indian subcontinent (where it is called a chital), it has been introduced to nations across the globe. It is considered an invasive species in some of these areas because it is a competitor for resources.2
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, giving them an advantage over many local species of deer.
While some invasive species have been introduced to certain areas as game animals, in their new environments, Axis deer 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 20% to 30% a year.3
Axis deer are highly social, and usually are found in herds ranging from a few animals to more than 100. Herd leaders 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
The breeding habits of axis deer are said to be similar to that of domestic cattle. In the wild, mature bucks in rutting condition may be found throughout the year, with each buck apparently having an independent reproductive cycle of its own, which may not be synchronized with that of other bucks in the herd.2,4 Does experience estrous cycles throughout the year, with each cycle lasting approximately 3 weeks. While pregnant females may be found year-round, most breeding lasts from mid-May through August. Bucks make no attempt to collect or retain harems of does.
The field immobilization of Axis deer is sometimes required for medical examination, blood sample collection, and animal identification, and the importance of performing such procedures for research and conservation projects is widely acknowledged.5,6 As these activities continue to become more common, the need to assess their negative effects increases in order to ensure ethical standards and the validity of research results. 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.5
Common stressors attendant to the chemical immobilization of Axis deer can lead to complications during or after an immobilization (sedation or anesthetic) event. The overall health of an individual animal is also a factor affecting the potential for complications during and after anesthesia.
These stressors fall into four categories:
Chemical immobilization agents are represented by the third category, although elements of the other three are often included in immobilization events. The physical stress of capture and/or attempts to escape during capture on the part of an animal certainly constitute physiological stress; surgical and even environmental conditions can bring about physical stress, and anxiety and fear are nearly always a component to some degree in a capture scenario.
Acute 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. The effects of capture and anesthesia can activate the fight-or-flight response, HPA-axis activation, hyperthermia, respiratory depression (hypoxemia), lactid acid build-up, acidosis; in severe cases, this can lead to neurological/myocardial dysfunction, multi-organ failure, capture myopathy and death.6
Compared to some surgical complications, dehydration may seem like a minor concern, but inasmuch as it can lead directly to cardiac arrest, dehydration (a significant reduction of the body’s water content) is potentially quite dangerous. All animals require water to ensure their bodies are working properly. It is so important that essentially all bodily functions require it to remain operative. 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 proper health. Electrolytes are comprised of sodium, chloride, and potassium, and facilitate the movement of nutrients into cells, aid in muscle function, and help regulate nerve activities.6,7 An animal’s natural activities—breathing, urinating, and defecating, as well as simple evaporation—all cause it to lose fluids. When an animal eats and drinks, the lost water and electrolytes are replaced. If the animal’s fluid intake becomes less than what they are losing, dehydration will occur. This causes a reduction in bodily fluids that reduces blood flow and the delivery of oxygen to organs and tissues.
An understanding of the distribution of fluid and water in the body is necessary in order to understand the dynamics of dehydration. Total body water (TBW) comprises approximately 60% of an animal’s body weight. Approximately 67% of TBW is found inside the body’s cells; this is referred to as intracellular fluid (ICF). The remaining 33% of TBW is the extracellular fluid (ECF), which comprises:
A simple approximate formula for the distribution of fluids in the body is the 60:40:20 rule:
Dehydration can be brought on by hyperthermia, chronic vomiting or diarrhea, excessive urination or wound drainage. Due to the stressful nature of capture and chemical immobilization events, all of these have been known to bring about dehydration. In both human and veterinary practices, IV fluids are usually administered prophylactically, depending on the nature of the procedure. Often, veterinarians will provide fluid therapy to patients for a variety of reasons, including correction of dehydration, expansion and support of intravascular volume, correction of electrolyte disturbances, and encouragement of appropriate redistribution of fluids that may be in the wrong compartment (e.g., peritoneal effusion).6
The available literature states that each species of deer has its own anesthesia recommendation with intra-species variations of dosages because of diverse individual responses to anesthetic agents.6,7 These variations are factors for the risk of dehydration in these species, and related factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account. Prior to the advent of some of the newer drug formulations, some hoofstock species were known to be notoriously difficult to immobilize successfully.
Monitoring core body temperature is essential in deer anesthesia.5 During anesthetic/immobilization events, hydration status can be assessed using various tests. One of the easiest to perform is 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 returns to its normal resting position. If the tent formed remains standing, it is a likely indication of dehydration. If there is evidence of dehydration in a deer 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 very common in veterinary medicine and allows practitioners to restore intravascular volume, correct dehydration, and administer IV medications quickly.6 While perioperative fluid therapy under many field conditions may be impractical, fluids should always be available in the case of dehydration when chemically immobilizing Axis deer.
1wildlifeinformer.com.
2J. Schmidly, J., Bradley, R. The Mammals of Texas, Seventh Edition 1994, University of Texas Press.
3tsusinvasives.org.
4animalia.bio.
5Laricchiuta 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.
64rivio 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.
7Kreeger T., Arnemo, J., Raath, J. Handbook of Wildlife Chemical Immobilization, International Edition, Wildlife Pharmaceuticals, Inc., Fort Collins, CO. (2002).