A bovine stress syndrome associated with exercise-induced hyperthermia

To investigate an exercise-induced bovine stress syndrome under field and controlled experimental conditions.

In the field study, cattle affected with the stress syndrome were observed while they were grazing and during normal mustering using horses. This study served to define the clinical nature of the syndrome. The experimental study utilised three affected and five normal unaffected cattle. These animals were compared on the basis of their response to a defined exercise program, which consisted of walking 3.6 km in 2 h. Blood samples and measurements of respiratory rate, ambient temperature and rectal temperature were taken immediately before exercise, and at 0.5, 1.0, 1.5 and 2.0 h during the exercise and 24 h later. Clinical and blood constituent data were subjected to standard analysis of variance and repeated measures analysis.

In the field study, affected cattle were observed to show abnormally anxious and hyperactive behaviour. This behaviour was exhibited by affected cattle during the experimental exercise program where it was shown to be accompanied by hyperthermia and hyperventilation. The experimental study showed that affected cattle developed metabolic acidosis and became hyperglycaemic. Their plasma creatine kinase activity remained markedly increased at 24 h after exercise but other clinical and blood constituent variables had returned to normal values.

The clinical and biochemical changes detected in affected cattle were consistent with exercise-induced malignant hyperthermia.