Behavioral and Physiologic Response to an Intermediate-Acting Tranquilizer, Zuclopenthixol, in Captive Nile Lechwe (Kobus megaceros)
Both free-ranging and captive (zoo) wild animals experience stress during periods of adaptation to new or changed surroundings and conditions.1 Though stress has no distinct cause or precise biologic measurement, evaluation of changes in behavioral and physiologic coping mechanisms allow some indication of stress.2 Behavioral coping mechanisms include movement from a threat to a more favorable location, vocalization, increased locomotion, aggression, and stereotypic behaviors. Observation of changes in behavior,3 heart rate,4-6 catecholamine, and corticosteroid5-7 levels may reflect “stress status” in animals.
Zuclopenthixol, a thioxanthene derivative, is a mid-duration neuroleptic, with pharmacologic effects within 1–12 hr of administration and lasting 72–96 hr in previously evaluated wild animals.8-10 Noticeable effects have included attitude modification toward surroundings and other captive animals (manifested as indifference), eating and drinking without inhibition, loss of instinctive fear of approaching humans, and relative calm adaptation to new situations.11
The objective of this study was to investigate the response of captive Nile lechwe (Kobus megaceros) to conditions surrounding typical shipment procedures while under the influence of a mid-duration neuroleptic, zuclopenthixol acetate (Clopixol-Acuphase® also known as Cisordinol-Acutard®, 50 mg/ml, H. Lundbeck A/S, Copenhagen-Valby, Denmark). The core study group consisted of five male and one female lechwe (two adults weighing 91–104 kg, four yearlings weighing 44–63 kg) with an additional two male sub-adults (estimated weight 86 kg) in trial #1 only from a herd of seven male adult, five female adult, and four undetermined-gender Nile lechwe. Animals were assigned randomly to one of two study groups while accounting for an even mix of ages. The study design provided for cross-over of the test (drug) and the control group for trial #1 and trial #2, which occurred 1 mo apart, allowing an interim return to the herd and rest period.
One month prior to trials, animals in the core study group were anesthetized for collection of baseline physiologic data, implantation of heart rate transmitters, and distinctive marking of individuals. Animals were anesthetized with carfentanil (dosage range: 17–24 µg/kg, Carfentanil, 3 mg/ml, Wildlife Laboratories, Fort Collins, Colorado, USA) and xylazine (0.19–0.36 mg/kg, Rompun®, Bayer Corporation, Shawnee Mission, Kansas, USA) i.m. by Telinject dart, supplemented with ketamine (0.80–1.13 mg/kg, Ketaset®, Fort Dodge Laboratories, Fort Dodge, Iowa, USA) i.v. upon initial handling to facilitate transport, intubated, and maintained on isoflurane (Aerrane®, Anaquest, Madison, Wisconsin, USA). The narcotic and sedative were antagonized with naltrexone (100x carfentanil dose divided 50% i.v. and 50% s.c., Trexanil®, Wildlife Laboratories, Fort Collins, Colorado, USA) and yohimbine (0.12–0.17 mg/kg, i.v., Antagonil®, Wildlife Laboratories, Fort Collins, Colorado, USA), respectively, prior to release into the herd. Heart rate transmitters (VHF-C-1 with 5000 Mah lithium batteries, Mini-mitter Co., Sunriver, Oregon, USA) were surgically implanted on the left dorsolateral thorax following an established technique12 with minor modification in lead placement. Heartbeat signals were monitored with a telemetry receiver (TR-2 fitted with the RA2AK flexible antenna, Telonics, Mesa, Arizona, USA). Dependent upon natural coloration, swatches of hair were bleached blonde or dyed black to assist in remote identification of subjects. Prior to the zuclopenthixol trials, baseline observations were collected for general behavior, resting heart rates, and fecal cortisol level for the subjects.
Lechwe were sorted into study groups and placed into adjacent paddocks (21x13 m area with 2.5 m wooden walls) for each 4-day trial. Behavioral and physiologic parameters were monitored by observation (direct and video camera for 12 continuous daylight hours), remote biotelemetric monitoring (intermittent), and laboratory testing of feces and blood. On day 1, zuclopenthixol was delivered into the biceps femoris muscle by Telinject® dart (5 cc vario syringe, 2.0x30 mm needle) to the test group at 1 mg/kg (45–105 mg) for trial #1 and 1.5 mg/kg (95–140 mg) for trial #2. Behavior and heart rate were monitored before, during, and after the application of various stressors. A fecal sample from each subject was collected daily for cortisol assay. The “manstand” stressor, characterized by 3 min of keeper presence within the paddock, was applied daily. Six hours were allowed to elapse after tranquilizer administration before the first “manstand” stressor was applied. The “chute” stressor, which involved herding the lechwe in each group singly from a raceway into a hydraulic squeeze chute for 10–15 min where the subjects were restrained for examination, phlebotomy, cervical tuberculin testing, and per rectum fecal collection, was applied on day 2. Venous blood was collected for CBC, serum biochemistry evaluation, plasma lactic acid assay, serum cortisol assay, and plasma catecholamine assay. Arterial blood was collected from an auricular artery for blood gas evaluation. The “novel item” stressor, characterized by release of subjects into a paddock containing a previously unseen 47 cm black trash can for 5 min, was applied on days 3 and 4. The subjects were returned to the main herd on day 4, greater than 74 hr after zuclopenthixol administration. General behavior was observed, random heart rates were recorded, and feces was collected for cortisol assay on days 5 through 7.
No undesirable extrapyramidal side effects or problems associated with zuclopenthixol were seen. Technical difficulties occurred with several transmitters, which did not allow collection of heart rate data for one subject in each trial and hampered precise consistent collection of heart rate data for two other subjects.
Differences were noted between the test (drug) and control group in several categories. Animals in the control group exhibited more pacing along fence lines, whereas animals in the test group were observed to spend more time eating and resting in sternal recumbency, particularly within the first 4–36 hr. Heart rates rose in all subjects during application of all stressors; heart rates remained elevated at a higher percentage of resting rate in control subjects in general throughout the chute restraint time period. Metabolic acidosis was observed on arterial blood gas evaluation for control subjects. Values for creatine phosphokinase and total bilirubin were elevated to a greater degree in control subjects. The administration of zuclopenthixol may serve as an adjunctive tool in stress reduction in some antelope species for 2–3 days.
The authors gratefully acknowledge the advice and assistance of Joe Vaughn, Steve Shurter, Dr. Lin Klein, Dr. Sue McDonnell, Dr. Bill Lance, Dr. Bengt Roken, and John Lukas. The hoofstock crew, veterinary preceptors, and certified veterinary technicians at the White Oak Conservation Center provided invaluable aid in handling of animals and samples. Monetary support for this project was provided by White Oak Conservation Center in support of the Graham-Gilman Residency in Wildlife and Zoological Medicine.
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