The agent of choice for wild equid immobilization and anesthesia is the potent opiate etorphine.3,5 A major advantage in the use of opiates is the specific opiate antagonists that allow for the complete reversal of the anesthetic effects.3,5 In North America, due to difficulty in obtaining etorphine, a similar, more potent opiate, carfentanil (Wildlife Pharmaceuticals, Fort Collins, CO, USA) has been used extensively in non-domestic equids.1,2 However, the quality of anesthesia from carfentanil are sometimes inferior to those of etorphine, including rough inductions and significant muscle contractions.
Here we present the field capture of six Przewalski’s horses (Equus ferus prezwalskii) in Hortobágy National Park, Hungary (www.hnp.hu/hu) and subsequent surgical anesthesia for the implantation of subcutaneous heart-rate telemetry units.
The horses were darted from foot or vehicle with a CO2 propelled dart gun (Daninject JM™, Wildlife Pharmaceuticals, Fort Collins, CO, USA) and 3 ml darts (Daninject, Wildlife Pharmaceuticals). A combination of 10 mg butorphanol (Torbugesic, Fort Dodge Animal Health, Fort Dodge, IA, USA), 10 mg detomidine-HCl (Domosedan, Orion Corp. Farmos Finland) and 0.7–1.4 mg ethorphine (M99, C-Vet Veterinary Products, Lancs, UK. This combination has previously been used successfully in wild Przewalski’s horses in Mongolia.4 Weights of the animals were estimated and ranged from 270–350 kg.
However, this chemical capture drug combination, at the doses provided, does not offer the necessary depth of anesthesia for surgical procedures as significant muscle contractions and uncontrollable movements can occur. Following dart administration, the horses became recumbent (n=4) or were pulled to the ground (n=2) in 5–10 minutes. In all cases, the head was controlled and a peripheral venous catheter was placed in the jugular or saphenous vein. Once the catheter was in place, an IV infusion of guaifenesin-ketamine-xylazine (1 L of 5% guaifenesin (Myolaxin, Vétoquinol UK Ltd, Buckingham, UK) 1000 mg ketamine (Ketamidor, Richter Pharma, 4600 Wels, Austria) and 500 mg xylazine (Rompun, Bayer Austria Ges.m.b.H, Vienna, Austria) was started. Nasal oxygen at a flow rate of 10 l/m was provided. Heart rate, respiratory rate, temperature, and saturation of hemoglobin with oxygen (SpO2) were measured and recorded every 5–10 minutes. Arterial blood gases were obtained at irregular intervals.
On average the duration of the procedure was 80 minutes after the initial dart. Depth of anesthesia was easily controlled with the triple drip combination and in all cases resulted in very good surgical anesthesia. The animals received on average 733 ml of the triple drip at an average rate of 12.6 ml/m. With exception of one individual that exhibited significant respiratory acidosis, monitoring data was satisfactory with SpO2 ranging between 71–94% and arterial pH never dropping below 7.3. However, despite oxygen supplementation all individuals where hypoxemic and slightly hypercapnic throughout the procedure.
Approximately 10 minutes before the surgical procedure was finished, the IV infusion was stopped. Subsequently, the opiate anesthesia components were reversed with 150 mg IV naltrexone (Wildlife Pharmaceuticals). All horses were standing 2–17 minutes after naltrexone administration. The alpha-2 agonist detomidine was not reversed.
The authors feel this multi-drug procedure is well adapted for surgical anesthesia in Prezwalski’s horses in a field setting. However, we strongly recommend that adequate anesthesia monitoring is available for the early recognition of critical respiratory and metabolic problems.
We acknowledge the support of the Cologne Zoo, Dr. Franz Schober in the initiation of this project, Dr. Waltraut Zimmermann, Moritz Zimmermann and Ing. Joep van de Vlasakker with help in the field.
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