Abstract
Capture and transport are essential procedures for the management and conservation of southern white rhinoceroses (Ceratotherium simum simum), but are associated with stress-induced morbidity and mortality. To improve conservation efforts, it is crucial to understand the pathophysiology of rhinoceros stress responses and investigate drug combinations that could reduce these responses. In this study we measured rhinoceros stress responses to capture and transport by quantifying hematological and immunological changes together with adrenal hormone concentrations. We investigated whether the potent anxiolytic drug midazolam was able to mitigate these responses compared to azaperone, which is more commonly used during rhinoceros transport. Twenty three wild white rhinoceros bulls were transported for 6 h (280 km) within the Kruger National Park for reasons unrelated to this study. Rhinoceroses were immobilized with either etorphine-azaperone (group A, n = 11) or etorphine-midazolam (group M, n = 12) intramuscularly by darting from a helicopter. Azaperone (group A) or midazolam (group M) were re-administered intramuscularly every 2 h during transport. Serial blood samples were collected at capture (TC), the start of transport (T0) and after 6 h of transport (T6). Changes in hematological and immunological variables over time and between groups were compared using general mixed models. Increases in plasma epinephrine and serum cortisol concentrations indicated that rhinoceroses mounted a stress response to capture and transport. Packed cell volume decreased from TC to T6 indicating that stress hemoconcentration occurred at TC. Neutrophils progressively increased and lymphocytes and eosinophils progressively decreased from T0 to T6, resulting in an increase in neutrophil to lymphocyte ratio; a characteristic leukocyte response to circulating glucocorticoids. A reduction in serum iron concentrations may suggest the mounting of an acute phase response. Rhinoceroses experienced a decrease in unsaturated fatty acids and an increase in lipid peroxidation products at capture and toward the end of transport indicating oxidative stress. Midazolam, at the dose used in this study, was not able to mitigate adrenal responses to stress and appeared to directly influence leukocyte responses.
Highlights
Translocation is the deliberate human-mediated movement of individuals or populations of wild animals from one location to another [1]
Rhinoceroses were weighed when placed in the transport crate and the drug doses used for the immobilization and sedation recalculated on a per kilogram basis
Descriptive analysis of results presenting mean ± standard deviation of the measured variables (PCV, red blood cell count (RBC), hemoglobin concentration (HGB), Packed cell volume (PCV), mean cell volume (MCV), mean cell hemoglobin (MCH), mean cell hemoglobin concentration (MCHC), red blood cell distribution width (RDW), PCT, platelet count (PLT), mean platelet volume (MPV), platelet distribution width (PDW), white blood cell count (WBC), BANDS%, SEG%, LYM%, MON%, EOS%, NEU, LYM, epinephrine, cortisol, N:L ratio, leukocyte coping capacity (LCC), triglycerides, phospholipids, conjugated diene (CD), thiobarbituric acid reactive substances (TBARS), oxygen radical absorbance capacity (ORAC), fibrinogen, haptoglobin, albumin, iron) at TC, T0 and T6 is shown in Supplementary Table 1 for the different groups
Summary
Translocation is the deliberate human-mediated movement of individuals or populations of wild animals from one location to another [1]. Despite the widespread use and importance of this practice, rhinoceros translocations often result in morbidity and even mortality [3, 4]. The two most frequently studied physiological systems orchestrating the stress response are the autonomic nervous system (ANS) and the hypothalamic-pituitary-adrenal (HPA) axis [8]. The response of the ANS to a stressor results in an almost immediate (milliseconds) increase in the release of the catecholamine neurohormone epinephrine from the adrenal medulla [10]. Stimulation of the HPA axis results in a slower (minutes) but more sustained release of the glucocorticoid steroid hormone cortisol (in mammals) from the adrenal cortex [10]
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