Abstract

Optimal hand-injected immobilization dosages of carfentanil/xylazine (CAR/XYL) were individually determined for 13 adult white-tailed deer. Deer were temporarily restrained in a squeeze chute and were repeatedly immobilized 1–4 times at 2–5-week intervals from December 2002–March 2003. A fixed ratio of 1 mg CAR:10 mg XYL intramuscularly was used, increasing or decreasing the dosage until the optimal dosage (defined by an induction time <3 minutes and PaCO₂ <60 mm Hg) was reached for each animal. Inductions were videorecorded and reviewed by observers blinded to drugs and dosages, who rated qualitative aspects of each induction.

The median optimal dosage (mOD) was 0.03 (range, 0.015–0.06) mg/kg CAR + 0.3 (range, 0.15–0.6) mg/kg XYL. Initial effects that would likely decrease post-darting movement in a field immobilization situation were noted in ≤1.6 minutes for all deer using the mOD. Induction times using the mOD were rapid (median 3.0 minutes [range, 1.8–10.0]) but quality ratings were considered “undesirable” for 9 of 13 deer. There were significant (p<0.05) dosage-dependent decreases in induction time, time to first effect (TE), PaO₂, SaO₂, and arterial pH, and significant dosage-dependent increases in PaCO₂ and quality ratings. Increased rectal body temperatures of 40.6±0.5°C (mean ± SD) were noted in all deer and hyperthermia (T>41°C) was noted in three. Heart rates significantly decreased from 5–15 minutes post-induction and remained decreased at the 20-minute reading; there was occasional bradycardia. There was a significant increase in pH from 10–20 minutes post-induction, but metabolic acidemia (pH<7.3) persisted throughout the immobilization periods for all deer. Hypoxemia (SaO₂<90 mm Hg) was present after induction but resolved by 20-minute post-recumbency; hypercapnia (PaCO₂>60 mm Hg) did not occur. Reversals with naltrexone and yohimbine were rapid (mean 3.7±1.5 minutes), complete, and uneventful, with no evidence of renarcotization.

This study successfully identified optimal dosages for all deer and demonstrated a CAR/XYL dosage-dependent linear relationship for both selected criteria (induction time and PaCO₂), validating the use of the iteration method. Additional study is needed to determine whether the optimal CAR/XYL dosage identified in this study is applicable to and safe for field immobilization of white-tailed deer.

Acknowledgments

This project was funded in part by The University of Tennessee, College of Veterinary Medicine, Hill’s Research Fund, and the University of Georgia McIntire-Stennis Project (GEO-0126-MS). Antler King Trophy Products, Inc., Moultrie Feeders, Inc., and Pennington Seed, Inc. made additional contributions. The authors gratefully acknowledge W. Lance of Wildlife Pharmaceuticals, Inc., and K. Kadidlo of Diametrics Medical, Inc., for contributions of drugs and materials used in this study. We thank students at University of Georgia for assistance with immobilizations; A. Saxton for performing statistical analyses; S. Dahmes, B. Harbison, and S. Harbison for recording and editing video footage; and R. Harvey and T. Doherty for rating of induction qualities.