We investigated the effects of a pre/per-exercise nutritional supplementation containing a high level of fat (medium and short chains fatty acids) and anti-oxidants (vitamins E, C and green tea polyphenols) on physiological and biochemical parameters, and on inflammatory and oxidative status of working dogs after exercise. Ten Belgian shepherds dogs, members of the Paris Fire Brigade K9 Search and Rescue Unit were randomly divided into two groups, in a cross-over designed protocol. They consumed 2g/kg body weight of the studied nutritional supplement or nothing, one hour before and in the middle of an endurance run test. After a fifteen day washout period, the trial was repeated by switching the two groups. Endurance test consisted of two times 20 minutes runs at a speed of 14km/h, separated by a passive rest of 5 minutes during which the supplement was provided to the concerned group. Physical parameters were measured before exercise (T0), at the end of the first 20 minutes run (T1), immediately after the end of the test (T2), and then at 10, 20, 30 minutes and 24 hours (T3) later. Blood samples were made at T0, T2 and T3. A smaller increase of the heart rate and a faster return to rest heart rate (10 min vs. 20 min) during and after exercise were observed in the supplemented group (SG) compared to control group (CG). Respiratory rate peak was lower in SG, and return to rest respiratory rate was faster (20 min vs. 30 min) in SG compared to CG. Thermal load tended to be lower after 20 minutes of run and at the end of the trial in SG compared to CG (39,2°C vs. 39,7°). After supplement ingestion, blood triglycerides were higher and decreased during exercise in SG. Advanced Oxidation Proteins Products (AOPP) were significantly higher at T2 in CG. No statistical difference was found for other oxidative stress related parameters. Interleukins IL1? and IL10 were statistically higher at T2 and T3 for CG. The results of this field study indicate that the tested nutritional supplementation lowers physiological modifications induced by this type of stamina in the dog. A slight decrease in the biological impact of exercise induced oxidative stress is observed through AOPP. Level of pro-inflammatory interleukins is higher post-exercise in the control group. Further experimentation is needed in order to better analyse the positive effect such nutritional supplementation versus exercise induced inflammation and their clinical consequences.