Abstract: REASONS FOR PERFORMING THE STUDY: As there are no reports on the real workload of horses that jump fences, this study was undertaken in riding-school horses. OBJECTIVE: To compare the workload of horses jumping a course of fences with that of horses cantering over the same course at the same average speed without jumping fences. The workload variables included heart rate (HR), packed cell volume (PCV), acid-base balance (venous pH, pCO2, HCO3-) and blood lactate (LA), glucose, total protein and electrolyte concentrations. METHODS: Eight healthy riding-school horses performed test A (a course of approximately 700 m with 12 jumps from 0.8-1.0 m high at an average speed of approximately 350 m/min) and test B (same course at the same speed, but without the rails) in a crossover study with at least 4 h between the 2 tests. Before each test the horses were fitted with a heart rate meter (Polar Electro). Blood samples were taken from the jugular vein at rest prior to the test, after warm-up before starting the course, immediately after the course and after recovery. All samples were analysed immediately. RESULTS: The mean +/- s.d maximal HR (beats/min) during the course (184 +/- 17 and 156 +/- 21, respectively) and the mean HR after recovery (75 +/- 6 and 63 +/- 7, respectively) were significantly higher in test A compared to test B (P = 0.001 and P = 0.007 respectively). The mean LA concentrations after the course and after recovery (mmol/l) were significantly higher in test A (3.6 +/- 2.7 and 1.0 +/- 0.9, respectively) compared to test B (0.9 +/- 0.5 and 0.3 +/- 0.1, respectively), (P = 0.016 and P = 0.048 respectively). The mean PCV (I/l) after the course and after recovery was also significantly different between tests A (0.48 +/- 0.04 and 0.39 +/- 0.03, respectively) and B (0.42 +/- 0.04 and 0.36 +/- 0.03, respectively) (P<0.01). The mean pH and the mean HCO3- (mmol/l) after the course were significantly lower in test A (7.40 +/- 0.04 and 28.9 +/- 1.4, respectively) compared to test B (7.45 +/- 0.03 and 30.4 +/- 2.3, respectively) (P<0.05). CONCLUSIONS: This study indicates that in riding-school horses jumping fences, even at a low level competition, provokes a significant workload compared to cantering the same distance and speed without fences. POTENTIAL RELEVANCE: This study makes it clear that the extra workload of jumping fences should be taken into account in the training programmes of jumping horses. Further research with more experienced horses jumping higher fences will reveal the workload for top-level jumping horses.