Abstract

In the past, immobilizations of free-ranging tapirs have utilized an etorphine/acepromazine combination (Immobilon®, Reckitt and Colman, Hull, England).^2,3 Problems with this protocol include the human safety hazard present when using etorphine, especially during night captures. The objective of this project was to devise an alternative anesthetic protocol that: 1) would be safe for the animals, 2) would be safer for the researchers, 3) would provide rapid induction, 4) would provide adequate immobilization, 5) was reversible, and 6) was relatively inexpensive. A butorphanol/xylazine combination was chosen because it fulfilled the above objectives and has been extensively applied and researched in the tapir’s close relative, the horse. The butorphanol/xylazine protocol afforded limited muscle relaxation; therefore, ketamine, another drug commonly used in the horse, was added to the protocol. This pilot study fulfilled two purposes: 1) to study the efficacy of the protocol for field situations and 2) initiate an in-depth look at the cardiopulmonary effects of the anesthetic protocol.

Twenty immobilizations of sixteen animals, using either butorphanol/xylazine or a butorphanol/xylazine/ketamine (Torbugesic®, Fort Dodge, Iowa, Rompun®, Bayer, Kansas, and Ketaset®, Fort Dodge, Iowa) protocol, were performed between March 1996 and February 1998. Due to field work logistics, actual body weights were only obtained on three subjects and thus weights were estimated. The purpose of the immobilizations was to radio collar the tapirs in order to record their habitat use, movement patterns and basic ecology. Biologic samples including ectoparasites, blood, skin biopsies, as well as rectal, vaginal and preputial cultures were collected at the time of immobilization. The tapirs were attracted to a capture area by using ripe bananas as bait. Tree platforms were constructed 30–40 feet above the capture area. Immediately after a tapir entered a capture area and began eating bananas, bananas were thrown from the tree platform, to maintain the tapir’s interest and continued to be thrown after the animal was darted. Animals were darted with a CO₂ rifle (DanInject® Wildlife Pharmaceuticals, Colorado) from the tree platforms. Darts (“P” type, Pneu-Dart Inc., Williamsport, Philadelphia) with 1.5 inch barbed or gelatin collared needles were used. The initial dart contained a mixture of butorphanol/xylazine. The doses of butorphanol ranged from 42–74 mg/animal, and the dose of xylazine ranged from 84–150 mg. In those cases where ketamine was utilized, it was delivered either intramuscular or intravenous via hand syringe following immobilization. Ketamine was used at 50–700 mg/animal. Intravenous ketamine was administered via a 20–22 g catheter in the auricular vein. The use and dose of ketamine was judged subjectively based upon the degree of sedation desired and the length of time needed for immobilization. Time from dart impact to first visible effect (ataxia, inability to prehend bananas), time to sternal recumbency and total immobilization times were recorded. Yohimbine (Yobine®, Lloyd Laboratories, Iowa) or tolazolene (Tolazine®, Lloyd laboratories, Iowa) was used to reverse the alpha-2 adrenergic agonistic effects of xylazine. Yohimbine was used at a dose range of 31–35 mg/animal. Tolazolene was used at 1120–1200 mg/animal. Naltrexone (Trexonil®, Wildlife Laboratories, Colorado) was used to reverse the opioid agonistic effects of butorphanol. It was used at 1120–1200 mg/animal. The reversals agents were administered intramuscular by hand syringe (Table 1). Time to return to sternal recumbency and time to standing were recorded.

Table 1. Individual anesthetic and recovery times

Key: Butorph.=butorphanol, Xylaz.=xylazine, Ketam.=ketamine, Yohim.=yohimbine, Tolaz.=tolazoline, Naltrex.=naltrexone
*Denotes actual body weight determined after anesthetic period

Heart rate, oxygen saturation as determined by pulse oximetry, indirect oscillometric arterial blood pressure, lead II electrocardiogram, and body temperature were measured using a portable bedside monitor (NPB-4000, Nellcor Puritan Bennett Inc., California). Pulse oximetry was applied to labia, prepuce, nasal planum or, most often, tongue. A cuff bladder width to forelimb circumference ratio of 40% was used for indirect arterial blood pressure determination. Respiratory rate was counted by direct observation of respiratory excursions. Arterial blood was obtained from the facial artery. Blood gas analysis was done with the use of a portable clinical analyzer (i-STAT, Sensor Devices Inc., Wisconsin). Blood gas analysis also included electrolytes, hematocrit and hemoglobin measurements. Percent cell volume was measured immediately after the captures as part of the blood processing. Each immobilization was rated with a subjective score based on induction, recovery and muscle relaxation.

Time from dart impact to first visible effect (ataxia, inability to prehend bananas) varied from 1–10 min. Time to sternal recumbency ranged from 4–24 min. The total time the tapirs were immobilized ranged from 13–60 min. Once the tapirs were given the reversal agents, the time to return to sternal recumbency ranged between 0–11 min and the time to stand ranged between 0–15 min (Table 2). Heart rates ranged between 28–108 beats/min. Respiratory rates measured between 8–21 breaths/min. Pulse oximeter readings varied between 54–100%. Indirect blood pressure measurements were between 101–202 mm Hg systolic and 66–127 mm Hg mean arterial pressure. Body temperatures remained within 35.5–40°C (Table 3). No irregular rhythms or arrhythmias were detected on electrocardiograms. Blood gas analysis findings on four individuals are summarized in Table 4. Induction, recovery and muscle relaxation ratings are summarized in Table 5.

Table 2. Individual immobilization and reversal drug doses

Key: T.=time, min=minutes
*Denotes animals that received ketamine

Table 3. Individual cardiopulmonary data

Key: HRT=heart, Resp.=respiratory, ECG=electrocardiogram, P=pressure, Temp.=temperature
*Denotes animals that received ketamine

Table 4. Individual blood gases data

Key: PCO₂=partial pressure of carbon dioxide, PO₂=partial pressure of oxygen, HCT=hematocrit, HBG=hemoglobin, BE=base excess, TCO₂=total carbon dioxide, SO₂=saturation of oxygen
*Denotes animals that received ketamine

Table 5. Individual recovery scores

Key:
Induction rating:
Poor=Animal walked away after having felt drug effects
Fair=Animal remained in bait area but acted nervous
Good=Animal remained in capture area until became immobilized but was aware of capture team
Exct=Same as a Good and animal continued to eat until sternal unaware of capture team
Recovery rating:
Poor=Animal was sitting up/standing when reversal was administered
Fair=Animal aroused prematurely, but did not sit or stand up prior to reversal
Good=Animal was not aroused prematurely but when reversed acted frightened and walked away
Exct=Animal was not aroused prematurely and upon reversal remained in bait area and resumed eating
Muscle relaxation rating:
Poor=Animal sat or stood up prior to reversal.
Fair=Animal voluntarily moved limbs or head, but did not sit or stand up prior to reversal
Good=Animal moved ears, mouth or vocalized but did not sit/stand up prior to reversal
Exct=Animal did not voluntarily move prior to reversal
*Denotes animals that received ketamine

The butorphanol/xylazine combination proved to be an effective method of immobilizing free-ranging Baird’s tapirs. Induction was relatively rapid; however, the use of bananas as bait was found to be crucial to the success of the induction period. Bananas ensured that the animal was less distracted by the dart and remained in the area until the drugs took effect. The butorphanol/xylazine combination provided sufficient sedation for radio collaring of animals; however, it was not of sufficient quality and duration to allow the extensive data and biologic sample collection. Loud noises, movement, pain, and other stimuli caused premature arousal. This is typical for low doses of an agonist/antagonist narcotic and an alpha₂-agonist combination in horses. The analgesic effects of xylazine do not typically last more than 45 min in horses.⁴ Close inspection of the data in Tables 2 and 5 illustrates that the use of ketamine 1)can be used to increase the immobilization period, and 2) provides a deeper sedation without changing the quality of the recovery described. Premature arousals were noted in animals on which either no ketamine was used, or the ketamine was administered at low doses i.m. The dose range of ketamine given i.v. to the last six animals immobilized ranged between 0.33 and 0.83 mg/kg (100–250 mg/animal). This dose was initially based on i.v. equine doses and subsequently on the subjective evaluation of the depth of sedation needed to manipulate the immobilized animals. The lower dose was sufficient for minor manipulations such as rolling the animal to lateral recumbency. Additional ketamine was utilized for major manipulations such as pushing or pulling the animal during measurements or sample gathering. Ketamine i.v. provided a more predictable outcome than ketamine delivered i.m. and did not reduce the quality of the recovery. Reversal of butorphanol/xylazine was achieved with either yohimbine/naltrexone or tolazolene/naltrexone. In our experience, no difference in reversal time was noted with tolazolene versus yohimbine, and thus, due to cost, tolazolene is preferred.

The cardiopulmonary effects of this protocol are reviewed in Tables 3 and 4. Due to the use of different dosing protocols, data cannot be grouped. Tapir normal heart rates are reported to be 45 beats/min.¹ The apparent decrease illustrated by some individuals can be attributed to the bradycardia caused by a reduction in central sympathetic tone caused by xylazine. Subjectively, one can note that heart rates were higher in those animals in which ketamine was used, which might be due to ketamine’s sympathomimetic effects. To our knowledge, respiratory rates of tapirs have not been reported; however, observed respiratory rates were within expected range for adult resting horses.⁴ Still, arterial partial pressure of carbon dioxide levels, when measured, were slightly elevated indicating hypoventilation. Indirect percent oxygen saturation as measured by pulse oximetry was less than the ideal 95% in several cases. This is probably due to the combined respiratory depressant effects of both xylazine and butorphanol, as well as the effect of recumbency on ventilation-perfusion matching. The tapirs in this project were kept lateral for more than half of their immobilization periods to accurately acquire morphometric measurements and have access to the medial saphenous vein. In those animals in which blood gas analysis was performed, the arterial oxygen saturation proved to be consistent with the pulse oximeter readings. Hypoxemia is defined in domestic mammals by an arterial partial pressure of 60 mm Hg.⁴ Although no animal reached this state, based on a limited number of blood gas measurements, some animals approached hypoxemic states. Blood pressure readings indicated that the mean arterial pressure was probably adequate for organ perfusion. Hematocrits, hemoglobin concentrations and electrolytes as measured by the portable clinical analyzer were within the normal ranges for Baird’s tapirs. Percent cell volumes were repeated immediately following the captures and correlated with the hematocrits provided by the clinical analyzer. Body temperatures also remained within normal values reported for tapirs.¹

In summary, a butorphanol/xylazine combination can be a safe protocol for the immobilization of free-ranging tapirs. It must be taken into account that it has the potential to produce a hypoxemic state and nasal insufflation of oxygen is recommended and planned for our future captures. Due to the short sedation period afforded by this protocol, the use of butorphanol/xylazine alone should only be utilized in immobilizations lasting less than 30 min. Ketamine is a safe agent that can be used to lengthen the immobilization period and aid in the depth of sedation. Since ketamine is not reversible and may produce undesirable side effects, one should allow enough time for ketamine to be redistributed prior to reversing the butorphanol/xylazine. An important side note is that this protocol has been utilized in animals that are relatively calm and focused on feeding. Alternative methodology may be necessary when tapirs are in a state of excitement.

Acknowledgments

This project was funded by a grant from San Diego Zoological Society and the Wildlife Conservation Society. Our sincere thanks to Dr. Don Janssen for his advice and support.

Literature Cited

1.  Lee AR. 1993. Management Guidelines for the Welfare of Zoo Animals - Tapirs. First edition. The Federation of Zoological Gardens of Great Britain and Ireland, London, England.

2.  Paras-Garcia A, Foerster CR, Hernandez SM, Leandro D. 1996. Immobilization of free ranging Baird’s tapir (Tapirus bairdii). Proceedings of the American Association of Zoo Veterinarians.

3.  Williams KD. 1979. Trapping and immobilization of the Malayan tapir in West Malaysia. The Malayan Nature Journal. Vol. 33, No.2: 117–122.

4.  Muir WW, III, Hubbell JAE. 1991. Equine Anesthesia. Mosby Year Book, St. Louis, MO.