Midazolam Alters Acid-Base Status Less than Azaperone during the Capture and Transport of Southern White Rhinoceroses (Ceratotherium simum simum)

SIMPLE SUMMARY: Capture and transport are important tools for rhinoceros conservation but are associated with morbidity and even mortality. Changes in acid-base status represent major life-threatening risks during rhinoceros capture and transport. In order to reduce these risks it is important to understand the nature of, and mechanisms contributing to, these acid-base changes. Usually, the tranquilizer azaperone is combined with the immobilizing drug etorphine for rhinoceros capture and is also administered as a tranquilizer during transport. In this study we describe changes in acid-base status during rhinoceros capture and transport and determine whether these changes can be reduced by administering the sedative midazolam, instead of azaperone. Twenty-three wild white rhinoceros bulls were captured with either etorphine-azaperone or etorphine-midazolam. During a 280 km road-transport, either azaperone or midazolam was re-administered every 2 h. All rhinoceroses experienced an increased acidity (low pH) in the blood (acidemia) during capture. Rhinoceroses captured with midazolam suffered less from acidemia than rhinoceroses administered azaperone. In all animals, recovery from the acidemia occurred rapidly after capture and pH remained within normal limits throughout transport. We show that using midazolam instead of azaperone, with the etorphine, may help reduce the risks associated with rhinoceros capture and thus, improve animal welfare during transportation operations. ABSTRACT: Acidemia represents a major life-threatening factor during rhinoceros capture. The acid-base status during rhinoceros transport is unknown. The purpose of this study was to describe changes in acid-base status during rhinoceros capture and transport and compare these changes between rhinoceroses sedated with azaperone or midazolam. Twenty-three wild white rhinoceros bulls were road-transported 280 km for reasons unrelated to this study. Rhinoceroses were captured with etorphine-azaperone (Group A) or etorphine-midazolam (Group M). During transport, azaperone (Group A) or midazolam (Group M) was re-administered every 2 h and venous blood collected. Changes in blood pH and associated variables were compared over time and between groups using a general linear mixed model. Rhinoceroses of both groups experienced a respiratory and metabolic acidosis during capture (pH 7.109 ± 0.099 and 7.196 ± 0.111 for Group A and Group M, respectively) that was quickly compensated for by the start of transport (pH 7.441 ± 0.035 and 7.430 ± 0.057) and remained stable throughout the journey. Rhinoceroses from Group M showed a smaller decrease in pH and associated variables at capture than rhinoceroses from Group A (p = 0.012). The use of midazolam instead of azaperone could therefore improve the success of rhinoceros capture and thus, contribute to the outcome of important conservation translocations.