The use of opioids in combination with an α-2 agonist has been previously described in a number of non-domestic hoofstock immobilizations.1,2,4,6,9 Since the development of A-3080® (Thiafentanil, Wildlife Pharmaceuticals, Inc, Fort Collins, CO, USA) in the early 90s, several protocols and dosages have been written for a wide spectrum of species with desirable effects during an immobilization.3,5-8,10 The effects of A-3080® have not been previously described on Tibetan yak (Bos grunniens).
Wildlife Safari houses a herd of 25 Tibetan yaks in an open setting, affording an opportunity to investigate this combination of drugs. A total of ten Tibetan yaks (Bos grunniens) were immobilized with thiafentanil and xylazine (TranquiVed® VEDCO, Inc., St. Joseph, MO, USA) for various medical procedures. This protocol was preferred over others used at the park previously for various reasons including faster induction, shorter duration of action, wide safety margin, fully reversible and lower cost.3,5,6,10 These characteristics are all desirable in an immobilizing agent, and are offered by A-3080®. Using these criteria, thiafentanil may be preferable when compared to carfentanil.
A Pneudart® rifle (Model 193, Pneu-Dart, Inc. Williamsport, PA, USA) and C-type darts were used to deliver the drug. The first drug effect (time of initial injection to initial drug effect) ranged from 2–4 min (average=3 min). The time from initial injection to lateral recumbency ranged from 4–8 min (average=6 min). Three of the ten yaks required additional A-3080® and xylazine due to dart malfunction or partial delivery of the drug. One of the ten yaks died under anesthesia due to compromised health status (poor body condition and chronic disease) and anesthetic complications.
A total of six male and two female yaks were immobilized with this protocol. One of the female yaks was darted on three separate occasions with the same combination of drugs, but different dosages. The doses were determined using estimated weights for all of the individuals. The six male subjects consisted of two juveniles and four sub-adults and ranged between 500 and 750 lb (227–340 kg). Of the two females in the study, one was a sub-adult and one was an adult, ranging in weight between 450 and 800 lb (204–363 kg). Actual weights were not recorded in any of the yaks. A range of 3.7–5.0 mg of A-3080® and 34–50 mg of xylazine were used for males. Female dosages were 4.0–7.5 mg of A-3080® and 30–50 mg of xylazine. An estimated median optimal dosage (mOD) was 0.018 mg/kg of A-3080® and 0.15 mg/kg of xylazine, with satisfactory results. Propofol was administered intravenously (IV) at an estimated dose of 1 mg/kg to maintain a light or surgical anesthetic plane. Short periods of apnea were observed on three of the ten yak after rapid administration of propofol. The apnea was treated by administration of doxapram IV at an estimated dose of 0.5 mg/kg. Vital parameters monitored included heart rate (HR), respiratory rate (RR), rectal body temperature, SPO2 (Pulse oximeter NELLCOR® N-20, NELLCOR® Inc., Pleasanton, CA, USA), blood gases (i-STAT®, Heska corp., Waukesha, WI, USA), complete blood count (CBC) and chemistry panel. Reversals with naltrexone (at dose of 50 mg of naltrexone for each 1 mg of A-3080®, ¾ of total dose given IM and ¼ of total dose given IV) and atipamezole (at dose of 1 mg of atipamezole for each 10 mg of xylazine, total dose IV) were rapid (3–5 min; average=4 min), complete, and without complications. No renarcotization effects were observed.
This study shows that the use of A-3080® and xylazine is an effective and safe option for the immobilization of Tibetan yak. Additional study is needed to determine whether the optimal A-3080® and xylazine dosages proposed in this study are the most effective dosages, and if this combination of drugs is suitable for use in wild Tibetan yak.
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