Abstract: Reliable physiological markers for performance evaluation in sport horses are missing. To determine the diagnostic value of plasma ACTH and cortisol measurements in the warmblood horse, 10 initially 3-yr-old geldings of the Hannovarian breed were either exposed to a training schedule or served as controls. During experimental Phase 1, horses were group-housed, and half of the horses were trained for 20 wk on a high-speed treadmill. During Phase 2, groups were switched and one group was trained for 10 wk as during Phase 1, whereas the control group was confined to boxes. During Phase 3 horses were initially schooled for riding. Thereafter, all horses were regularly schooled for dressage and jumping, and half of the horses received an additional endurance training for 24 wk. During all phases horses were exposed at regular intervals to various standardized treadmill exercise tests. During and after the tests frequent blood samples were taken from an indwelling jugular catheter for determination of ACTH and cortisol. Treadmill exercise increased both hormones. Maximum ACTH concentrations were recorded at the end of exercise, and maximum cortisol levels were recorded 20 to 30 min later. Except for one test there were no differences in ACTH levels between trained horses and controls. There was no significant effect of training on the cortisol response (net increase) to treadmill exercise in any of the tests during Phase 1. During Phase 2 higher cortisol responses were recorded in controls than in trained horses (P < .05) after 10 wk of training (controls confined to boxes). During Phase 3 plasma cortisol responses were also higher in controls than in trained horses (P < .05 after 6, 18, and 24, P < or = .07 after 12 wk of training) when the inclination of the treadmill was 5%, but not at 3%. There was no overlap in net cortisol responses at 30 min between trained and untrained horses. An ACTH application after 24 wk of training resulted in higher cortisol responses in controls than in trained horses (P < or = .05), without any overlap between the groups at 30 min after ACTH. Plasma cortisol responses to either treadmill exercise or ACTH injection may be a reliable physiological marker for performance evaluation. Prerequisites are sufficient differences in training status and sufficient intensity of exercise test conditions.

Abstract: We examined the effects of participation in each of 3 modifications of Day 2 of a 3-day-event on blood and serum variables indicative of hydration, acid:base status and electrolyte homeostasis of horses. Three groups of horses – 8 European (E) horses and 2 groups each of 9 North American horses performed identical Days 1 (dressage) and 3 (stadium jumping) of a 3-day-event. E horses and one group of the North American horses (TD) performed modifications of Day 2 of a 1 Star 3-day-event and the other group of North American horses (HT) performed a Horse Trial on Day 2. Jugular venous blood was collected from each horse on the morning of Day 2 before any warm-up activity, between 4 min 55 s and 5 min 15 s after Phase D and the following morning. Eight E horses, 5 TD horses and 8 HT horses completed the trials. There were few significant differences in acid:base or serum biochemistry variables detected among horses performing either 2 variations of the Speed and Endurance day of a 1 Star 3-day-event, or a conventional Horse Trial. Failure to detect differences among groups may have been related to the low statistical power associated with the small number of horses, especially in the TD group, variation in quality of horses among groups and the different times of the day at which the E horses competed. Differences detected among time points were usually common to all groups and demonstrated metabolic acidosis with a compensatory respiratory alkalosis, a reduction in total body water and cation content, and hypocalcaemia. Importantly, horses of all groups did not replenish cation, chloride, and calcium deficits after 14-18 h of recovery.

Abstract: Body weight of 48 horses competing in a 3-day event was measured the day before the event (baseline), following the dressage phase of the event (day 1), after the endurance phases of the event (day 2), and 18 to 24 hours after the endurance phases (day 3). Plasma sodium and potassium concentrations were measured the evening before, immediately after, and 10 minutes after the endurance phases. Total body water, water loss, and net exchangeable cation loss were then calculated. Body weight and total body water were significantly decreased, compared with baseline values, at all times during the event, and significant water loss was detected. The largest changes were recorded after the endurance phases of the event. Water deficits were still detected 18 to 24 hours after the endurance phases of the event. Mean plasma sodium concentration was significantly increased immediately after the endurance phases of the event, compared with concentration measured the evening before, and remained increased after the 10-minute recovery period, presumably because of dehydration. Mean plasma potassium concentration was significantly increased immediately after the endurance phases of the event, compared with concentration measured the evening before, but was not increased after the 10-minute recovery period.

Abstract: The time-motion characteristics of Canadian basic- and medium-level dressage competitions are described, and the results are applied in formulating sport-specific conditioning programs. One competition was analyzed at the six levels from basic 1 to medium 3. Each test was divided into a series of sequences based on the type and speed of activity. The durations of the sequences were measured from videotapes. The basic-level tests had fewer sequences, and they were shorter in distance and duration than the medium tests (P < 0.10), but the average speed did not differ between the two levels. It is recommended that horses competing at the basic levels be conditioned using 5-min exercise periods, with short (10-s) bursts of lengthened trot and canter included at basic 2 and above. In preparation for medium-level competitions, the duration of the work periods increases to 7 min, 10- to 12-s bursts of medium or extended trot and canter are included, and transitions are performed frequently to simulate the energy expenditure in overcoming inertia.

Abstract: The object of this study was to determine the limb support sequence during the transitions from walk to trot and from trot to walk in dressage horses under saddle and to test the null hypothesis that the limb support sequence during the transitions is not related to the level of training. Sixteen dressage horses training at novice to FEI Grand Prix level were videotaped performing an average of 9 transitions each from walk to trot and from trot to walk. The 30-Hz videotapes were viewed in slow motion, and based on the limb support sequence the transitions were categorized into two types. In type 1 transitions there were no intermediate steps between the walk and trot sequences. Type 2 transitions were characterized by intermediate steps, including a single support phase. The Kendall rank-order correlation coefficient showed that a higher level of training was positively associated with an increased percentage of type 1 transitions for both walk-to-trot transitions (p < or = 0.05) and trot-to-walk transitions (p < or = 0.01). No significant preference for initiating or completing the trot on the left or right diagonal was found using the binomial test for individual horses and the Wilcoxon signed-ranks test for the group.