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.
