Physiological responses to capture and transport in southern white rhinoceros (Ceratotherium simum simum) and southern-central black rhinoceros (Diceros bicornis minor)

Abstract

The southern-central black rhinoceros is currently listed as “critically endangered” and the southern white rhinoceros as “near threatened” by the International Union for Conservation of Nature Red List of Threatened Species. Translocation is an important tool for rhinoceros conservation and is widely used to reinforce declining populations or to restore extirpated populations. Capture and transport are part of translocation and expose the rhinoceros to a variety of stressors that ultimately can lead to morbidity and mortality. The broad objectives of this thesis were therefore to: (1) establish a better understanding of the physiological responses to capture and road-transport in African rhinoceros, (2) to identify challenges associated with transport that should be addressed in order to improve animal welfare, and (3) to investigate whether the use of midazolam, instead of azaperone, would be able to mitigate some of these challenges. The third chapter of this thesis investigated physiological responses to capture and long road transport in black and white rhinoceros in a “real-world” setting. Paired venous blood samples were collected from an auricular vein at capture and after transport in 14 boma-adapted black, and 32 semi-captive white rhinoceros and were evaluated for changes in: (1) clinical chemistry analytes; (2) acute phase reactants and (3) oxidative stress biomarkers. The Wilcoxon rank sum test was used to compare changes in measured analytes from capture and after transport. The fourth and fifth chapter explored some of these changes in more detail and investigated if there were differences between rhinoceros sedated with midazolam compared to azaperone. Twenty-three wild white rhinoceros bulls were captured with a combination of etorphine plus either azaperone or midazolam. Azaperone or midazolam, respectively, were re-administered intramuscularly at capture (TC), start of transport (T0), and at two (T2) four (T4) and six (T6) hours of transport. Acid-base status was evaluated at these time points. Adrenaline and cortisol concentrations, as well as haematological (erythron, thrombon, leukon) and immunological (leukocyte coping capacity, acute phase reactants and oxidative stress biomarkers) changes, were measured at TC, T0 and T6. Changes in measured variables over time and between groups were compared using general mixed effects models. Black and white rhinoceros transported over a long time experienced total body water loss, mobilisation of energy reserves, muscular damage, and stress-induced immunomodulation. White rhinoceros bulls experienced respiratory acidosis combined with a lactic- and non-volatile weak acid acidosis during capture, followed by a mild metabolic- and strong ion alkalosis during transport. Increases in plasma adrenaline and serum cortisol concentrations indicated that rhinoceros mounted a stress response to capture and transport. The stress response was associated with characteristic haematological and immunological changes including stress-haemoconcentration, a progressive increase in neutrophil to lymphocyte ratio, the mounting of an acute phase reaction and oxidative stress. The acidaemia and associated alterations in acid-base indices were significantly less pronounced in midazolam-sedated compared to azaperone-sedated rhinoceros. Plasma adrenaline and serum cortisol concentrations did not differ between the groups. Midazolam, however, appeared to greater influence immunological responses to stress than azaperone. Based on these results, we identified the following challenges to animal welfare during rhinoceros capture and transport: (1) life-threatening acid-base abnormalities associated with the unique challenges of rhinoceros capture; (2) fear and the mounting of a stress response to capture and the novelty of transport; (3) stress-induced immunomodulation; and (4) skeletal muscle fatigue, energy imbalance and dehydration that likely become more relevant with transport time. Midazolam proved to be able to partly mitigate the first challenge and may therefore be a safer alternative to azaperone when combined with etorphine for the capture of wild white rhinoceros. Further research looking at behavioural benefits of using midazolam over azaperone, and possible consequences of its immunological effects, are required to demonstrate the value of midazolam administrations during transport. To optimise rhinoceros translocation, additional measures that aim to mitigate challenges to animal welfare during capture and transport, such as administering fluids during long journeys, need to be included in the planning of future translocations. The effectiveness of these measures in mitigating these challenges need to be systematically investigated.