Comparison of thiafentanil-azaperone and etorphine-azaperone for the immobilisation of free-ranging black rhinoceros (Diceros bicornis)

Abstract

This study aimed to determine the efficacy, safety and cardiorespiratory effects of etorphine, azaperone and hyaluronidase (EA treatment) vs thiafentanil, azaperone and hyaluronidase (TA treatment), for immobilization of free-ranging black rhinoceros (Diceros bicornis). Comparing and determining whether one of these drug combinations resulted in a more effective and safer immobilisation of black rhinoceros, will allow improvements in the welfare and conservation of these animals, and thus also ensuring the safety of personnel involved in such capture events. In this randomised, prospective field study, twelve male and twelve female, adult, black rhinoceros were included. Animals were randomly immobilised with EA (n = 12) or TA (n = 12). The dose administered was based on age group and sex of the animal. Treatments were administered intramuscularly via remote dart injection. Induction, immobilisation and recovery times and scores were recorded and compared between treatments. Respiratory rate, heart rate, rectal temperature, oxygen haemoglobin saturation and arterial blood pressure were measured at 5-min intervals for 30 minutes. Arterial blood gases were obtained and measured every 10 minutes. Significant faster induction times were recorded in the TA group (2.88 ± 0.75 minutes) compared to the EA group (3,95 ± 0.77 minutes). Immobilisation was successful in all animals. The heartrate (HR) and blood pressure decreased significantly in both groups over time. Both the use of TA and EA resulted in a reduced PaO2 and increased PaCO2, but no differences were observed between or within treatments. An increased alveolar to arterial oxygen gradient was noted in both treatments. Acidaemia, decreased base excess and bicarbonate levels, hypercapnia and hyperlactatemia indicated that respiratory and metabolic lactic acidosis occurred in both treatments. Both combinations provide an acceptable induction, immobilisation and recovery for black rhinoceros, however, hypoxaemia, hypercapnia and acidosis occurred. Safety was evaluated based on cardiorespiratory parameters and the absence of adverse effects during immobilisation and recovery. Either etorphine or thiafentanil with azaperone and hyaluronidase, can therefore safely be used for the immobilisation of black rhinoceros. The use of the thiafentanil combination can provide a faster induction, minimising run time, potentially reducing stress and overexertion, and their associated metabolic derangements.