Anesthesia of pronghorns using thiafentanil or thiafentanil plus xylazine

Thiafentanil is a potent synthetic opioid anesthetic being developed for wi ldlife 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 dosa ges of either 4.0 or 5.0 mg of thiafentanil without (group 1) or with (grou p 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 gro ups for capture times or physiological parameters (P greater than or equal to 0.21). Anesthetic induction was rapid for both groups (less than or equa l to 2.7 +/- 0.4 min) as was recovery after antagonism (less than or equal to 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 resp iration. Twenty-five pronghorn were radiocollared and survived greater than or equal to 21 days after capture. One adult male in group 1 died during c apture. Thiafentanil was considered more effective on pronghorn than carfen tanil-xylazine, ketamine-xylazine, or tiletamine-zolazepam-xylazine anesthe tic regimens.