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¹ Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tennessee 37996-4544, USA
² Warnell School of Forest Resources, University of Georgia, Athens, Georgia 30602, USA
³ Corresponding author (email: larktim{at}teleport.com)

ABSTRACT:   Using an iteration method, optimal hand-injected immobilization dosages of carfentanil/xylazine (CAR/XYL) were determined for 13 adult white-tailed deer (Odocoileus virginianus). Deer were temporarily restrained in a squeeze chute and were repeatedly immobilized one to four times at 2–5-wk intervals from December 2002 to 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 min and PaCO₂< 60 mmHg) was reached for each animal. Inductions were videorecorded and reviewed by observers blinded to drugs and dosages, who rated qualitative aspects of each induction. There were significant (P<0.05) dosage-dependent decreases in induction time, time to first effect, PaO₂, SaO₂, and arterial pH, and significant dosage-dependent increases in PaCO₂ and quality ratings. 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. Induction times using the mOD were rapid (median 3.0 min [range, 1.8–10.0]), but quality ratings were considered undesirable for nine of 13 deer. 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. There was a positive correlation between body temperature and induction time (r=0.44). Heart rates significantly decreased from 5 to 15 min postinduction and remained decreased at the 20-min reading; there was occasional bradycardia. There was a significant increase in pH from 10 to 20 min postinduction, but metabolic acidemia (pH<7.3) persisted throughout the immobilization periods for all deer. Possible hypoxemia (SaO₂ and SpO₂<90 mmHg but PaO₂>60 mmHg) was present after induction, while hypercapnea (PaCO₂>60 mmHg) did not occur. Reversal times with naltrexone and yohimbine were rapid (mean 3.7±1.5 min) and uneventful, with no evidence of renarcotization. Although the median optimal dosage produced rapid inductions, no respiratory depression, complete reversal after antagonist administration, and no renarcotization, negative attributes included elevated body temperatures, acidemia, and undesirable induction qualities.
  Key words:  Carfentanil, cervid, iteration method, Odocoileus virginianus, optimal dosage, white-tailed deer, xylazine.