Anesthesia of Pronghorns Using Thiafentanil or Thiafentanil Plus Xylazine

Thiafentanil is a potent synthetic opioid anesthetic being developed for wildlife anesthesia. Thiafentanil was tested for safety and efficacy on free-ranging pronghorn (Antilocapra americana) inhabiting F. E. Warren Air Force Base in southeastern Wyoming. Pronghorn were darted with pre-measured dosages of either 4.0 or 5.0 mg of thiafentanil without (group 1) or with (group 2) the addition of 25.0 mg xylazine. Seventeen pronghorn were captured in group 1 and 14 pronghorn in group 2. There were no differences between groups for capture times or physiological parameters (P ≥ 0.21). Anesthetic induction was rapid for both groups (≤ 2.7 ± 0.4 min) as was recovery after antagonism (≤ 0.7 ± 0.07 min). The dosage of thiafentanil administered was 0.10 ± 0.005 mg/kg and the dosage of xylazine was 0.56 ± 0.03 mg/kg. Anesthesia in both groups was characterized by muscle rigidity and rapid, shallow respiration. Twenty-five pronghorn were radiocollared and survived ≥21 days after capture. One adult male in group 1 died during capture. Thiafentanil was considered more effective on pronghorn than carfentanil-xylazine, ketamine-xylazine, or tiletamine-zolazepam-xylazine anesthetic regimens.