Gregory J. Fleming, DVM, DACZM
Disney's Animal Programs and Environmental Initiatives, Lake Buena Vista, FL, USA
Immobilization of artiodactylids or hoof stock can be challenging, but can also be complete in a safe, reproducible manner for many species. Hoof stock in itself is a term which includes many species such as gazelles, antelopes, bovids, deer, giraffes and even equids. The wide range of variability of these species habitats, lifestyles and even body mass, results in multiple approaches to immobilization for each and every species. Of course, this cannot be covered in this review; however, we will cover the basics and some drug dosage options for some species.
Most often when discussing immobilization of hoof stock, veterinarians conjure up the idea of darting or using a blow pipe to deliver the drug. In fact, in many situations this may be the preferred and only option to deliver the drugs safely and effectively. However, other options such as drop floor chutes, squeeze cages, hand grab and hand injection all play their role in drug delivery.
1. Hand restraint and hand injection – this is often a great option for small hoof stock such as muntjac all the way up to Impala. The advantage of this technique is that the option for immobilizing drugs increases significantly as intravenous access is now possible. The disadvantage is that you need a well designed facility with a drop chute and experienced personnel. Without both of these, animals may get injured.
2. Drop Chute – Hydraulic or manual drop chutes or "tamers" are available commercially and are great options in many cases for minor procedures or to allow for intravenous or intramuscular injections. The advantage is that they can fit small hoof stock 20 kg all the way up to 800 kg. Disadvantage is that even with experienced personnel, animals can get easily overheated or become traumatized when entering or exiting the tamer. Many of the tamers are portable which allows for maximum use.
3. Remote injection – This is often the safest and most reliable method of dart delivery for medium and large hoof stock. Many remote dart systems are available commercially and all have different options. Depending on your level of expertise, some systems are more fool proof than others, and if used only occasionally take minimal upkeep.
a. Pneudart systems: medium to long range darting. This system utilizes gun powder charges both in the delivery system and the dart. In addition, these darts come in premade, one time use, and in variable volume sizes. This system is very versatile and can be used for long distances as well as in bommas. The great benefit of this system is that the darts are only used once and do not need any upkeep. Once a dart is used it must be discarded. However, for someone only using a dart system occasionally this may be a good option. The major disadvantage to Pneudart is that on small species (30 kg) and a close range (15 meters) the power of the delivery may be too strong.
b. Telinject and Daninject systems use compressed air for both the dart and the delivery of the drug. Both of these systems and have different types of delivery options including pistol style with short and long barrels and rifle for long distance shots. In up close zoo environments this is the preferred drug delivery system as the dart delivery pressure can be adjusted to be very low which enables darting within 3 meters. The major disadvantage to these systems is that the darts are reusable. Darts must be broken down and cleaned after each use. With dart cleaning and reassembly, comes human error, which may result in dart failure if not done correctly.
Remote injection equipment:
In some instances using a pole syringe may be all that is needed to get a drug delivered. There are two basic types, manual and mechanical:
1. A manual pole syringe is basically a long pole that inserts directly into the syringe case and needs to be manually injected (via the operator) by pushing the needle into the animal and then pushing the plunger of the syringe to the hub, in one motion. This system works well for small volumes (< 3ml). With larger volumes (> 3ml) animals usually react in the time it takes to depress the plunger resulting in partial injections. However, this system is good choice for giving vaccines.
2. Mechanical pole syringes have a spring loaded injection system that pushes the plunger of the syringe in, once the needed is inserted into the animal. This system is better for larger volumes and results in fast injections. The main disadvantage is that the pole itself is heavier than the manual pole and is not as easy to use.
When using hand restraint, pole syringes or remote drug delivery systems, there is a potential for injury to both the veterinarian and the animal. It is in the best interest of anyone who is not familiar with this type of equipment to obtain some experience by shadowing at a zoo, taking continued education at a conference, or taking a wildlife immobilization course. In many cases, the drugs used to immobilize hoofstock are very concentrated and may have serious implications for health if injected into a person. Concentrated drugs such as etorphine, carfentanil, thiafentanil and even medetomidine can cause immediate and life threatening consequences if injected into a human or even applied to mucous membranes.
These drugs should be handled with great care using personal protective equipment such as gloves, and eye protection. Used darts should be placed in protective cases and cleaned by veterinarians or technicians trained in using these concentrated drugs. Even dart sites on animals can contain enough residual drugs to cause serious medical problems. People working on/near animals immobilized with these drugs should be wearing latex gloves and be trained in clinical signs of human exposure and the potential side effects. At the author's facility, the emergency kit includes a human emergency crash kit containing oxygen, intubation materials, opioid reversals and a human defibrillator in case of accidental exposure. It is most prudent to notify the local hospital that you are using these concentrated drugs in case of accidental exposure.
Selection of specific drug combinations is the art of immobilizing hoof stock. The scope of this lecture does not allow for a complete review of the drug selection. However, based on the author's experience, immobilization of hoof stock falls into 2 categories: immobilization with concentrated opioids and immobilization without concentrated opioids. In any case, each species poses its own special risks and tricks. The best option is to invest in a few good reference books and start with published doses and modify them to suit your own needs.
Immobilization with Concentrated Opioids
Opioids include drugs such as M99 (etorphine), carfentanil, thiafentanil, and fentanyl. They have been commonly used but have a variety of side effects that must be taken into account.
Advantages: Highly concentrated, very potent, reliable signs of restraint, handled during onset and specific antagonists.
Disadvantages: Safety concerns for administration, special DEA licensing, side effects including respiratory depression, muscle rigidity, hypertension, bradycardia, decreased GI motility, regurgitation and re-narcotization.
To mitigate the side effects of opioids they are often combined with other drugs, such as alpha 2 agonists (xylazine, detomidine and medetomidine), phenothiazines (acepromazine) and butyrophenones (azaperone, haloperidol). The goal is to increase muscle relaxation and reduce side effects of hypotension and respiratory depression. In addition, drugs such as ketamine, propofol, guaifenesin and volatile gas anesthesia can all be used in combination with concentrated opioids to achieve immobilization.
Different Anesthetic Protocols for Impala
Carfentanil 30-40 µg/kg IM
Xylazine 0.2-0.3 mg/kg IM
M99 50-70 µg/kg IM
Xylazine 0.15-0.25 mg/kg IM
Medetomidine 30 µg/kg IV
Ketamine 3 mg/kg IV
Midazolam 50 µg/kg IV
Propofol 3-5 mg/kg IV
Isoflurane gas 2-5% via endotracheal tube
Immobilizations without Concentrated Opioids
This includes the use of mixed opioids, such as butorphanol which is a partial agonist and antagonist. This drug has a slower onset and will not cause complete immobilization if used alone. It is often paired with other drugs, such as such medetomidine and azaperone. This combination is commonly referred to as "BAM" and has been growing in popularity since in many species such as white tail deer the combination works very well.
Advantages: BAM does not have a concentrated opioid and thus is more practical for many veterinarians to use, provides good muscle relaxation, completely reversible, and rapid recovery.
Disadvantages: In hoof stock, the concentrated medetomidine is now available which has allowed for darting of large hoof stock. This concentrated medetomidine (up to 50 mg/ml) should be handled very safely as it may be as dangerous as concentrated opioids due to its highly concentrated state. This combination also has a short length of duration (30-40 min) without supplementation. Arousal and short duration can be overcome by adding ketamine or volatile gas anesthesia to the anesthetic protocol. Arousal is possible with the short duration of effect is limited to 30-40 min.
Butorphanol 0.3-0.62 mg/kg
Azaperone 0.30-0.41 mg/kg
Medetomidine 0.18-0.25 mg/kg
Naltrexone 2-5x the butorphanol dose (in mg)
Atipamezole 5 x the medetomidine dose (in mg)
Butorphanol 25-35 µg/kg
Detomidine 25-35 µg/kg
(45 min duration)
Haloperidol 0.05-0.2 mg/kg (variable by species and individual)
(12 hour duration)
Zuclopenthixol 0.6 mg/kg (variable by species and individual)
(1 hour- 3 days)
Trilafon 0.4-0.7 mg/kg (variable by species and individual)
(1.5 day delay up to 7days duration)
Anesthetic monitoring is one of the most underutilized tools in wildlife immobilization. In many cases, a new species is being immobilized, or the veterinarian performing the immobilization may have limited experience with that species. This stresses the importance of anesthetic monitoring.
Without any fancy equipment the best monitoring can be with a stethoscope and a thermometer. Respiration, heart rate, circulation, response to stimuli and body temperature should be evaluated every 5-10 minutes and recorded. This will allow you to act accordingly and modify your anesthesia.
Arterial Blood Gas Analysis
This is the gold standard for monitoring oxygen, carbon dioxide and phi There are multiple options available for this type of equipment, however to be effective it must be portable for field operations. The author uses an ISTAT system which is a small hand held unit that has a selection of cartridges that plug into the machine and can test for different variables including blood chemistries. This system works very well but has limited temperature parameters in which to work. (60F-85F).
Normal blood gas and pH
pH = 7.40; Range 7.35-7.45
PaO2 = 95 mm Hg, Range 80-110 mm Hg, Hypoxemia PaO2 < 70 mm Hg
PaCO2= 40 mm Hg, Range 35-45 mm Hg, Hypercarbia PaCO2 > 50 mm Hg
Pulse oximetry is the noninvasive measurement of oxygen bound to hemoglobin. It is measured via a light emitting probe and provides real time, continuous and immediate information regarding blood oxygen levels. Developed for human use, this technology must be adapted for our hoof stock patients. The probe may be used on an ear, lip, scrotum, labia and even an eyelid. In species with dark skin this technology may not work as the melanocytes interfere with the probes light scores. In some species like black rhino, if you scrape the ear with a scalpel blade and then apply the pulse oximetry probe it will often pick up a reading. Care must also be taken to realize that the oxyhemoglobin dissociation curve drops off fast and a reading of 90 and 80% SaO2 may have magnitude difference in oxygen levels. Normal levels should be above 95% saturation. Pulse oximetry levels will be elevated with the addition of oxygen, but this must be balanced with CO2 levels to get a true picture.
Capnography (End-Tidal CO2)
Capnography measures the amount CO2 being removed during exhalation. Most units show a capnogram which characterizes the length and depth of the inspiratory phase. This is helpful in characterizing how the animal is breathing. Some capnography units are handheld and are available with a built-in pulse oxymeter. These units are very helpful in that they are often more predictive of respiratory problems than pulse oximetry alone. SaO2 levels will be increased with oxygen supplementation but CO2 levels can also remain high leading to a respiratory acidosis despite good oxygen supply.
Blood lactate is a measure of the transition from aerobic to anaerobic metabolic activity. Over-exertion and inadequate oxygen or perfusion of blood will lead to an elevated lactate level. Lactate levels < 2.5 mmol/L are considered normal. Lactic acidosis or hyperlactatemia causes a decrease in blood pH which is a precursor to capture myopathy. With the advent of small portable and inexpensive lactate analyzers for the human athlete field, this measurement can be easily taken with a single drop of blood. A good rule of thumb is to take a measurement at the start, middle and end of the procedure to see if a trend is developing. High lactate at the start of the procedure may indicate over exertion and should slowly decrease over the length of the procedure. If lactate is critically high > 15 mmol/L supportive measures such as IV fluid with bicarbonate should be undertaken.
In any case don't allow sophisticated devices to remove your attention from the patient! Use your eyes, ears and stethoscope to monitor what is actually going on with your patient.
Monitoring depth of anesthesia can be accomplished through assessment of palpebral, corneal, and anal reflexes. Changes in eye position, muscle relaxation, jaw tone and tongue and ear movements are the first sign and animal is too light or too deep.
Intubation of hoof stock can be challenging as they often have narrow and deep dental arcades. Intubation can be accomplished by using a stylette and the Murphy eye of the endotracheal tube. This usually takes 3-4 people to be successful. Using a strap or gauze on the lower and upper jaw, the assistants open the mouth and tip the head backwards pointing the nose into the air. The tongue is pulled forward and the stylette, which is threaded through the Murphy eye of the endotracheal tube, is passed into the epiglottis. Once the trachea is visualized, thread the stylette into the trachea, then pass the endotracheal tube over the stylette into the trachea. Sometime the endotracheal tube may need to be one size smaller than a perfect fit to go over the stylette.
In any case hoof stock immobilization can be challenging and also rewarding. Each clinician must develop his/her own anesthetic style and technique. This lecture is just a small view into anesthesia of exotic artiodactylids. To study this topic further, please make an investment and refer to the references provided or enroll in an immobilization wet lab or course.
1. Caulkett N, Shurry T. (2007). Human Safety during wildlife capture. Zoo Animal and Wildlife Immobilization and Anesthesia. Blackwell Scientific, Oxford UK. Pg 123-131.
2. Kock MD, Meltzer D, Burroughs R. (2006) Chemical and Physical Restraint of Wild Animals. A Training and Field Manual for African Species. IWVS, Greyton SA. Available in the USA from Wildlife Pharmaceuticals www.wildpharm.com.