Physiology of capture myopathy

Abstract

This investigation has been carried out in three nature reserves in the Transvaal, the Kruger National Park and in two game reserves in Natal. Specimens for trace element analysis were collected also from Natal and from three Lowveld nature reserve complexes. A study of 104 individuals of nine species of animals after locomotory stress indicates that the primary cause of mortality after a short (2 km) chase is a profound acidaemia, with muscle pH significantly lower than that of central venous blood. There was a s·ignificant correlation between pH and blood lactate. Systemic changes include aberrations in the electrocardiogram configuration associated with hyperkalaemia, depression of calcium ions, tachycardia (up to 350 beats per minute), hypotension and a pulmonary arterial hypertension. High capillary haematocrit together with low P02 , pH and high PC02 indicated peripheral stasis. A rise in the haematocrit of central blood after restoration of the blood pH by infusion of bicarbonate indicated a return of sequestrated blood to the circulation. Plasma myoglobin and haemoglobin showed a significant correlation with distance run. There was a significant rise in blood potassium to near lethal levels. Reduced kidney function due to vasospasm, relieved by alpha-blockade with phenoxybenzamine hydrochloride, is believed to predispose to tubular blockade with blood and muscle pigments as demonstrated at autopsy. High levels of GOT, GPT, CPK and LDH were seen in all animals subjected to locomotory stress (except in trained animals). There was a significant difference between stress due to transport and exercise stress. Investigation of liver content of trace elements on a seasonal basis revealed a significant correlation between chlorine, cobalt, magnesium, sodium and zinc. Major differences were determined exceeding 200 percent in the seasonal variation of selenium as well as copper, cobalt and other essential trace elements. Highly significant differences were apparent in enzyme peaks between the first and subsequent runs. Differences were also seen in plasma haemoglobin and myoglobin between animals run for the first time, and after several dummy or training runs at low speed. It is concluded that preliminary exercising of animals and their familiarisation with capture methods and corrals is the best prophylactic against stress during capture.