Rapid reversible immobilization of feral stallions using etorphine hydrochloride, xylazine hydrochloride and atropine sulfate.

This study tested the use of certain drugs to quickly and reversibly immobilize wild and captive stallions. They found that the use of etorphine hydrochloride, xylazine hydrochloride and atropine sulfate was effective, but the method of administration and certain combinations impacted the time of immobilization and recovery. Tragically, three horses died during the study for a variety of reasons.

Research Method and Objectives

• The purpose of this research was to examine the effectiveness of various drug combinations (etorphine hydrochloride, xylazine hydrochloride and atropine sulfate with or without acepromazine) for the immobilization and subsequent revival of feral stallions. The study sought to devise a method for quick and reversible immobilization for various applications.
• They tested the drug combinations on 48 wild stallions that had recently been caught, from two different locations, and six stallions held in captivity. Six animals underwent the procedure twice, a month apart.
• The drugs were administered either by intramuscular (i.m.) injection (n = 13) or intravenous (i.v.) injection (n = 44).

Findings of the Study

• The study found that the average time to immobilization was significantly quicker when the drugs were administered intravenously (55 +/- 4 sec) as compared to intramuscular injections (708 +/- 131 sec).
• Reversing the immobilization was done using diprenorphine hydrochloride and yohimbine hydrochloride, administered intravenously. The average time to revival and standing was 86 +/- 7 seconds after administration of reversal drugs.
• The study noted that using an equal amount of diprenorphine to etorphine was as effective as a 2:1 ratio of diprenorphine to etorphine for reversing the immobilization.
• The addition of Acepromazine had no significant effect on the induction time but it was found to decrease relaxation after immobilization and extended the time of ataxia after the reversal of etorphine and xylazine.
• Eight horses were successfully immobilized by darting with a combination of the drugs from a helicopter, taking an average of 708 +/- 132 seconds.

Unfortunate Casualties

• However, the research was marked by the tragic loss of three animals. One animal died immediately after reversal from intravenous administration, the second perished from a broken neck during the induction from darting, and the third was found dead a week later at the site of darting.