Effect of altitude on plasma serotonin levels in horses

The aim of this work was to carry out a preliminary study about the effect of the altitude differences on horse plasma serotonin (5-HT) and tryptophan. Horses came from riding school a.s.l. and 600 m a.s.l. To evaluate animal welfare linked to physiological status, cortisol levels with blood cell count and haematochemical variables (glucose, total proteins, albumin, creatinine, urea, aspartate transaminase, creatine kinase, lactate dehydrogenase, triglycerides, total cholesterol) have been detected. Comparison of mean plasma levels of 5-HT, tryptophan and cortisol in horses coming from different altitudes did not show significant changes. Plasma 5-HT levels were affected by altitude in a gender-dependent way, showing an opposite trend between mares and geldings and the highest levels in plasma of geldings coming from farms a.s.l. Both 5-HT and tryptophan amounts showed greater values in mares than in geldings from 600 m a.s.l.. Plasma cortisol levels, higher in mares than in geldings, significantly a.s.l., were more affected by gender than altitude