Haematological, biochemical and physiological changes in horses and ponies during the cross country stage of driving trial competitions.

The haematological, biochemical and physiological changes associated with the cross-country stage of driving trials were studied in horses and ponies competing in singles, pairs, tandems and teams at five, five-section and two, three-section events. Heart rates were monitored continuously and sometimes exceeded 200 beats/minute. The highest maximum, mean and recovery heart rates were found after the most severe competitions. Rectal temperatures were also highest after the most severe events and in some animals exceeded 41 degrees C. Respiratory rates were very variable. Blood taken five minutes after the cross-country showed a marked increase in haematocrit and a leucocytosis. Total plasma protein concentration increased by about 9 per cent but there was little change in the concentrations of plasma electrolytes. There was a very variable increase in plasma lactate concentration, the increase being related to the severity of the event; plasma lactate concentration occasionally exceeded 10 mmol/litre. Plasma glucose was also increased. The activities of plasma creative kinase and aspartate aminotransferase were only slightly increased after the cross-country stage.