Dehydration in Deer During Capture and Chemical Immobilization

There are over 60 species of deer that are recognized worldwide, and deer occur on all continents except Antarctica. 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

Deer are hoofed mammals which belong to the order Artiodactyla; these animals are also known as cervids. Male deer are referred to as bucks, although species of larger males are often called stags. Female deer are called a does or hinds, and young deer are called fawns. Bucks and does can be distinguished from each other by the presence or absence of antlers. Female Caribou (also known as Reindeer) are the only female deer which grow antlers.

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. Except in the case of caribou, female deer do not grow antlers. While the antlers grow, they are covered by a thin layer of downy skin known as velvet. When the antlers are fully grown, the velvet dries and is typically rubbed off by the animal.² Antlers serve as ornamentation for breeding purposes, as well as weapons during the mating season.

Deer have a four-chambered stomach, and are cud-chewing herbivores, or ruminants. Cud-chewing is a process of partially chewing food, swallowing and regurgitating it, then chewing it again to make it easier to digest.

Deer can have a homeland range which can cover up to 30 miles, and they typically move about depending on food availability.

Deer and Chemical Immobilization

The field immobilization of 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.¹ 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.²

There are a number of common stressors attendant to the chemical immobilization of deer that 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:

• Physiological: Heavy exercise, hemorrhage, hyperthermia, shock, pain, infection
• Physical: Trauma/surgery, intense heat/cold
• Chemical: Hypoxemia, acid-base imbalance, anesthetic drugs
• Emotional: Anxiety, fear³

Obviously, 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.

The effects of 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.⁴

Dehydration Risks in Deer

On its face, dehydration may seem like a minor concern compared to some surgical complications, but inasmuch as it can lead directly to cardiac arrest, dehydration (a 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.^3,4 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.

Understanding Dehydration in Deer

To understand dehydration, one must first understand the distribution of fluid and water in the body. 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:

• 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)²

A simple approximate formula for the distribution of fluids in the body is 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.^2,3

Dehydration can be caused by hyperthermia, chronic vomiting or diarrhea, excessive urination or wound drainage. Due to the stressful nature of capture and chemical immobilization events, they 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. Veterinarians often provide fluid therapy to 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 that may be in the wrong compartment (e.g., peritoneal effusion).²

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.^2,3 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.

Treating Dehydration in Deer

Monitoring core body temperature is essential in deer anesthesia.³ 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.³

Perioperative IV fluid therapy is very common in veterinary medicine and allows practitioners to restore intravascular volume, correct dehydration, and administer IV medications quickly.⁴ While perioperative fluid therapy under many field conditions may be impractical, fluids should always be available in the case of dehydration when chemically immobilizing deer.