In all Equestrian sports, the welfare of the horse must be paramount and must never be subordinated to competitive or commercial influences. It is necessary to prohibit any train-ing methods which are abusive or cause fear or for which the horse has not been properly trained. The purpose of this study was to examine the effects of prolonged and intensive physical training on the immune response in trotter horses in order to recommend at the legislator the adoption of guidelines for the welfare of these animals. In fact, during their athletic life and some of them undergo lethal lung infections, therefore it is likely that modi-fications of physiologic cellular parameters could account for the increased susceptibility to microbial disease. Noteworthy, chronic stress has been shown to be immunosuppressive, whereas acute stress seems to lead to immunoenhancing effects. In particular, we have stud-ied some immune parameters as blood cells distribution, hemoglobin, hematocrit, erythro-cyte sedimentation rate, phagocytosis activity, macrophage Migration Inhibiting Factor (MIF) and finally the levels of (1-3)-ß-D-Glucan, as indicator of clearance. Taken together, these findings indicate a condition of reduced immune response in seven trotters after race, to identify possible biomarkers of stress dependent on physical exercise.