Aspiration in Axis Deer During Capture and Chemical Immobilization

The Axis deer (Axis axis) is a deer species that is native to the Indian subcontinent, although they have been introduced into approximately one dozen other countries, including the United States and some European nations. It is a visually striking animal with a spotted body and short tail.¹

The body of the Axis deer is a golden brown in color with the head being a bit lighter in shade. They have stripes of fur that are paler in color around the eyes. Males have black spots on their faces and three tines on each of their three-foot antlers. Both males and females have white markings which run in rows along the length of their bodies. They also have a dark stripe running along the length of their backs which are bordered by a row of spots. Their undersides are typically cream-colored or white; they have white spots on the throat and a white underside to the tail. Male axis deer weigh from 66–165 lbs (30–75 kg), and females weigh 55–99 lbs (25–45 kg). Males are larger than females, and antlers are present only on males.²

The Axis deer’s period of highest activity is in the morning and late afternoon.³ During the day, the Axis deer can usually be found resting in the shadows. They tend to remain near water, drinking in the mornings and evenings. Axis deer are always on the alert, in anticipation of a sudden appearance of a predator. They are vocal animals that will emit bellows and barks of alarm. Females and juveniles will bark persistently when alarmed or if they see a predator.

Axis deer are herbivores, with a diet consisting of grasses, flowers, and fruit that has fallen from trees. In their native range during the monsoon, grasses and sedges become the main source of food for these animals.³ They will also eat mushrooms that are rich in proteins and nutrients.²

Axis deer are sociable animals, with herds comprised of from 6–30 individuals. Most larger herds will have two or three stags. Males live in a hierarchical system with larger and older males dominating smaller and younger ones.³ Mature females and their fawns typically form matriarchal herds. Axis deer are polygynous, meaning that a male will mate with multiple females. During mating season, males will start bellowing, which signals the beginning of breeding, which takes place in April or May. The Axis deer’s gestation period lasts 210–225 days. They produce young every year, with females giving birth to 1 or 2 fawns at once. Females will nurse fawns until they are 6 months old, and the young become reproductively mature at the age of 12-14 months.^1-3

Axis Deer and Aspiration

Wildlife managers, deer farmers and researchers are often called upon to perform routine procedures on Axis deer, or to administer medical treatment. In nearly all cases, this requires the use of sedative and/or anesthetic drugs. Vomiting is one of the more common post-sedation and post-anesthesia complications in both domestic and exotic animals. Vomiting that occurs during a procedure can pose grave risks due to anesthetic aspiration.

Aspiration is when a foreign substance enters the airway or lungs. This can apply to food, liquid, or other materials. This can give rise to serious health problems, such as aspiration pneumonia. Aspiration can occur when an animal has difficulty swallowing normally (which is referred to as dysphagia), but in some instances it can be brought on during or after immobilization events.

Aspiration pneumonia is a condition that is characterized by inflammation and subsequent necrosis of lung tissue due to the inhalation of foreign material. The most common materials aspirated in large animals are liquids, due to weakness from a pathological condition, during oral administration of fluids or as a result of chemical immobilization. The severity of the inflammatory response depends upon the type and volume of material aspirated and the distribution of aspirated material in the lungs.

In severe cases of aspiration, death can occur swiftly. Other cases will present later with clinical signs consistent with cranioventral bronchopneumonia.³ Cervids such as Axis deer that are affected with chronic wasting disease may also develop aspiration pneumonia due to central nervous system dysfunction.⁴

Axis Deer and Chemical Immobilization

At the beginning of the last century, the primary method used for the capture of many large wild animals such as deer was to chase them to the point of near-exhaustion—a labor-intensive method that was impractical and fairly inhumane.⁴ With the pioneering work on the chemical immobilization of wildlife that took place from the 1950s on, chemical immobilization techniques have improved greatly through the development of increasingly efficacious drugs and equipment.

The field immobilization of deer with chemical agents is a method of rendering them tractable while using minimal restraint. The research or wildlife management objectives are usually to measure or weigh the live deer, collection of blood or tissue for research or diagnostics, marking an individual or fitting a radio transmitter for studying migration patterns, range requirements and behavior patterns or the translocation of animals for a variety of reasons.^4,5 These requirements have resulted in the development of increasingly safer methods of chemical immobilization.

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 These variations are of course factors in the risk of vomiting and anesthetic aspiration in these species, and attendant factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account.

Chemical Immobilization Practices and Procedures

The utilization of basic veterinary knowledge can make a substantial contribution to animal safety during capture and chemical immobilization. Teams that are qualified to handle wild mammals should evidence the appropriate expertise in wildlife anesthesia and should include an attending veterinarian when appropriate. A successful chemical restraint exercise is not complete until the subject is fully recovered and (in the case of field operations) back in its environment. The application of appropriate pharmacological principles with an emphasis on drug reversibility will minimize the chances that the animal will be at a competitive disadvantage or inordinately disoriented following its release.^4-6

Hyperthermia and capture myopathy are commonly-encountered problems with deer anesthesia. Intubation has been widely recommended for any anesthetized deer that needs to be transported or anesthetized for greater than one hour. Unfortunately, the literature strongly suggests that intubation can increase the risk of vomiting during an anesthetic event.^4,6

Managing Anesthetic Aspiration in Axis Deer

Until formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents) came into use in recent years, opioids were the mainstay of large animal anesthesia in wildlife and captive care.⁷As with other mammals, problems encountered with certain opioids (such as etorphine or carfentanil, which have been widely used in wildlife chemical immobilization) in deer are known to include vomiting or passive regurgitation that can lead to fatal aspiration pneumonia.

Fasting prior to an anesthetic event (periprocedural fasting) has historically been recommended by clinicians because of the risk of aspiration. Unfortunately, periprocedural fasting is very often impossible under field conditions. Additionally, much of the data on anesthetic aspiration relates to humans receiving general anesthesia, however, Axis deer and other mammals have been known to aspirate during procedures while under sedation and where no intubation or general anesthesia were employed.

To prevent anesthetic aspiration, the literature recommends histamine (H2) antagonists such as cimetidine, famotidine, nizatidine, and ranitidine and proton pump inhibitors (PPIs) such as dexlansoprazole, esomeprazole, lansoprazole, omeprazole, pantoprazole, and rabeprazole, which have been shown to be effective in increasing the pH and reduce the volume of gastric contents.⁴ Prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are also believed to reduce the risk of aspiration.⁵

In the event that aspiration in an Axis deer occurs during a procedure, the first step in managing the situation is the recognition of gastric content in the oropharynx or the airways.^6-8 The deer should be immediately positioned with the head down and rotated laterally if possible. Orotracheal and endotracheal suctioning is indicated, either before or after orotracheal intubation, depending on whether regurgitation continues and if the airway is visible. It is recommended that the airway be secured as rapidly as possible to prevent further contamination and to facilitate airway clearance.⁴ Flexible bronchoscopy is an important adjunct to orotracheal and endotracheal suctioning. Rigid bronchoscopy may be required if particulate matter is present in the deer’s airway.^4,7