Chemical immobilization and blood analysis of feral horses (Equus caballus).

The study explored different combinations of etorphine hydrochloride and xylazine hydrochloride as immobilizing agents on captured wild, feral mares. It indicated that the optimal combination for their capture in the field, administered from a helicopter, included 5.5 mg of etorphine hydrochloride, 150 mg of xylazine hydrochloride, and 3 mg of atropine sulfate in a 7-ml dart syringe. The study discussed the horse mortality rate, blood sample results, and costs related to this capture method.

Chemical Immobilization of Feral Horses

• A total of 16 feral mares that were recently captured and placed in corrals underwent testing with various combinations of etorphine hydrochloride and xylazine hydrochloride to find an effective immobilizing agent.
• The optimal combination for field capture included 5.5 mg of etorphine hydrochloride, 150 mg of xylazine hydrochloride, and 3 mg of atropine sulfate in a 7-ml dart syringe.
• This combination was used to successfully capture 87 free-ranging feral horses from roughly 80 bands, delivered from a dart gun fired from helicopters.

Results and Analysis

• The study reported a mortality rate, with five mares dying at the time of capture and the remains of three others found near the capture site four months later.
• Blood samples were collected and analyzed for hematologic variables, and concentrations of urea and glucose. The results produced values that were comparable to domestic “hot-blooded horses.”
• The serum cortisol concentrations from the captured horses were comparable to the levels found in undisturbed captive animals, suggesting that the stress induced by the capture method was not excessive.

Expenditures

• On average, approximately 48 minutes of helicopter time were necessary per each captured horse.
• The total cost per animal captured summed to approximately $159 for helicopter time and an additional $66.70 for the necessary drugs and darts.