Low-dose thiafentanil in combination with azaperone alone or azaperone and medetomidine for the immobilization of African buffalo (Syncerus caffer)

Abstract

Objective To determine the efficacy, safety and cost of a novel drug regime comprising of a low thiafentanil dose in combination with medetomidine and azaperone; to the more established thiafentanil and azaperone combination for the immobilization of African buffalo (Syncerus caffer)

Study design Prospective, randomised, cross-over study.

Animals Twelve adult African buffalo (Syncerus caffer) bulls.

Material and methods This randomized cross-over study on twelve African buffalo (Syncerus caffer) was performed on a buffalo farm located in the Sekhukhune District Municipality, Limpopo, South Africa. The study consisted of two data collection periods. The two combinations used were the more conventional thiafentanil-azaperone (TA) drug combination comprising of thiafentanil oxalate at 6-7 mg/animal and azaperone at 40 mg/animal as described by Burroughs et al. (2012b), and the novel thiafentanil-medetomidine-azaperone (TMA) combination comprising of a relatively low dose of thiafentanil oxalate at 1 mg/animal, medetomidine hydrochloride at 3-4 mg/animal and azaperone at 40 mg/animal. During the first data collection period, each buffalo was immobilized once with either the TA or the TMA combination. Six buffalo received the TA combination and six buffalo received the TMA combination. After twenty-one days, each buffalo was immobilized with the alternate combination. One animal was immobilized at a time. Before each data collection period, the animals were brought from the breeding camps into the boma where food and water was withheld for 24 hours and 12 hours respectively to minimize the risk of regurgitation during immobilization. For the immobilization and data collection, the respective buffalo was separated from the herd and moved into a separate pen. The buffalo were dosed according to its estimated weight and body condition score (BCS) as visualised by the immobilisation team. After dart placement, a stopwatch was started and the time to immobilization as well as quality of induction was recorded. Once recumbent, the animal was instrumented with a digital rectal thermometer (HI98509 Checktemp 1, HANNA Instruments (Pty) Ltd., USA), a pulse oximeter (Veterinary Pulse Oximeter, Model 9847V, Nonin Medical, USA) to measure the peripheral oxygen haemoglobin saturation (SpO2) and a multi-parameter monitor (M3T Mini vet, TooToo Meditech, China) which was used to measure the end-tidal carbon dioxide (ETCO₂). The caudal auricular artery was aseptically cannulated for continuous arterial blood pressure measurement using an intra-arterial blood pressure monitor (IntraTorr, IntraVitals, United Kingdom) and blood sampling. Blood was drawn at 10-, 20- and 35-min post immobilization and was analysed on site with a portable blood gas analyser (epoc® SIEMENS Blood Analysis System, Siemens Healthcare GmbH, Erlangen, Germany) using single-use epoc® BGEM Test Cards. Physiological values and anaesthetic plane were recorded at 5-min intervals until 40 minutes. Variables measured were the heart and respiratory rate, body temperature, SpO₂ and ETCO₂. After 40 minutes, the buffalo was de-instrumented, antagonized and the recovery times were recorded. The TA combination was antagonized using naltrexone hydrochloride intravenously at 10 mg/mg thiafentanil. The animals immobilized with the TMA combination received a standardized mixture of atipamezole and yohimbine intravenously at 0.5 ml/mg medetomidine hydrochloride followed by naltrexone hydrochloride at 10 mg/mg thiafentanil. The immobilization costs were compared descriptively.

Results The mean dosages (range) of the thiafentanil-azaperone combination were 0.0136 (0.011 to 0.0163) mg kg-1 thiafentanil and 0.0792 (0.063 to 0.093) mg/kg azaperone; and of the thiafentanil-medetomidine-azaperone combination were 0.00216 (0.0016 to 0.0023) mg kg-1 thiafentanil, 0.00688 (0.0047 to 0.0084) mg/kg medetomidine, and 0.0688 (0.047 to 0.084) mg/kg azaperone. The TA combination induced recumbency in a significantly shorter time compared to the TMA combination. Mean (range) induction times for the TA and TMA combinations were 5.7 (4 - 9.5) and 10.95 (6 - 20) minutes, respectively. Both combinations provided sufficient immobilization throughout the procedure of 40 minutes for routine veterinary and management procedures. Heart rates were significantly different (p < 0.001) between the two combinations with a mean heart rate of 139 bpm (± 25) and 70 bpm (± 27) in the TA and TMA combination, respectively. There was a significant difference in the PaO₂ (p < 0.05) between the two combinations. All buffalo were hypoxaemic during immobilization with a mean (SD, range) PaO₂ value of 44 mmHg (± 14, 24 – 77 mmHg) and 51 (± 13, 33 – 80 mmHg) in the TMA and TA combination, respectively. The A-a gradient was significantly different (p < 0.01) between the two combinations and was significantly wider in the TMA than in the TA combination: TMA (mean, ±SD): 40 (± 9) mmHg; TA (mean, ± SD): 27 (± 13) mmHg. The costs to chemically immobilize and antagonise an adult buffalo bull using the TA combination were ± R 593/buffalo. This is four times more expensive than the TMA combination which was calculated at ± R 146/buffalo.

Conclusions and clinical relevance Both combinations were effective in providing a sufficient immobilization for routine veterinary and management procedures in African buffalo with quick recoveries and no mortalities. The TMA combination induced immobilization with only 1/7th of the higher dose of opioid and at only a quarter of the cost. Hypoxaemia was a concern in both combinations and resulted mainly from decreased pulmonary oxygen diffusion rather than hypoventilation. Importantly, despite respiratory rates and partial pressure of carbon dioxide (PaCO2) values being within the normal expected physiological range, hypoxaemia was more severe in the TMA combination. Supplementary oxygen is considered mandatory during immobilisation with both combinations. The enormous reduction in costs with the TMA combination could be beneficial for the wildlife industry. However, the longer induction times, and risks from marked hypoxaemia need to be considered and addressed when this combination is used.