Effects of surgery on endocrine and metabolic responses to anaesthesia in horses and ponies.

The effects of surgery on endocrine and metabolic responses to anaesthesia were investigated in seven horses and eight ponies. They were anaesthetised twice and surgery was carried out on one occasion. Cardiorespiratory monitoring was performed and blood samples were taken for assay of cortisol, glucose, lactate, insulin, catecholamines and non-esterified fatty acids. All groups developed arterial hypotension which was more marked in the surgical groups where post operative pulse rate was also higher. Plasma cortisol concentration increased in all groups during anaesthesia but remained higher after surgery. Plasma lactate increased in all animals but was higher during surgery. Glucose, insulin and catecholamines did not change significantly during anaesthesia in the horses but NEFA decreased. Plasma glucose increased during anaesthesia in the ponies and was higher in the non-surgical groups. The study suggests that surgery has little additional effect on the stress response to halothane anaesthesia in Equidae.