Abstract: REASONS FOR PERFORMING STUDY: Equine lameness is commonly evaluated when the horse is being ridden, but the influence of the rider on the lameness has not been documented. OBJECTIVE: To document the effect of 2 riders of different training levels on the vertical movement of the head and croup. METHODS: Twenty mature horses were ridden at trot by an experienced dressage rider and a novice rider, as well as trotted in hand. Kinematic measurements of markers placed on the horse's head and sacral bone were carried out. The asymmetries of the vertical head and sacral bone motion were calculated as lameness parameters and compared with paired t tests. RESULTS: Trotting in hand, 17 horses showed forelimb lameness (1-4/10) and 13 hindlimb lameness (1-2/10). Intra-individually, 11 horses showed significant differences in forelimb lameness and 4 horses showed significant differences in hindlimb lameness when ridden. Over all horses, hindlimb lameness increased significantly under the dressage rider compared to unridden horses. CONCLUSIONS: The presence of a rider can alter the degree of lameness; however, its influence cannot be predicted for an individual horse. POTENTIAL RELEVANCE: In order to evaluate mild lameness, horses should be evaluated at trot both under saddle and in hand. If lameness is exacerbated, a second rider may be helpful; the level of training of the rider should be taken into consideration.

Abstract: Changes in social hierarchy were evaluated in a herd of 3-year-old Hanoverian geldings. One group (n = 5) was exposed to a training programme, the other (n = 5) remained untrained. After 6 months, the groups were reversed. Hierarchical positions were evaluated by field observations and/or paired-feeding tests at the beginning, the middle, the end of the first and at the end of the second training period. Both methods yielded identical results. Almost all horses changed position in only one direction: either up or down. Neither increase in aggression nor mutual injuries were recorded during the whole experiment. No statistically verified differences in dominance ranking occurred between trained and untrained groups, but apparent differences were consistent. Thus, if horses are kept in the same group for a longer period of time, exercise induced changes in hierarchy are probably of minor importance and are unlikely to increase the incidence of injuries. This may have implications for the promotion of group-housing for sport horses.

Abstract: Feeding and training may affect acid-base responses to strenuous exercise. Acidosis usually correlates with higher blood lactate concentrations during intense exercise, but alkalosis has been found in several studies of horses, and higher lactate responses during sprints have been found in fat adapted horses. To elucidate these unexpected findings, we applied a comprehensive physicochemical approach to evaluate acid-base responses during exercise in fat adapted horses. In incremental tests and repeated sprints, changes in blood [H+] were dependent upon corresponding changes in pCO2 but not strong ion difference (SID, the algebraic sum of ions of sodium, potassium, chloride and lactate). The influence of changes in [Lac-] were largely offset by changes in [Na+], [K+] and [Cl-], so that SID was unchanged and did not contribute to the exercise induced acidemia, so it may be inaccurate to term this a lacticacidosis. During repeated sprints, central venous [H+] increased (acidosis) but arterial [H+] decreased (alkalosis). These changes were consistent with concurrent changes in venous and arterial pCO2 but not SID. Fat adaptation decreased mixed venous pCO2 during repeated sprints, which is consistent with the lower respiratory quotient associated with fat oxidation. Less pulmonary work to eliminate CO2 could benefit horses under hot and humid conditions, especially those with mildly reduced pulmonary function. The blood lactate response was decreased during aerobic tests but increased during anaerobic tests on fat adapted horses. Fat adaptation appears to facilitate the metabolic regulation of glycolysis, by sparing glucose and glycogen at work of low intensity, but by promoting glycolysis when power is needed for high intensity exercise. The blood lactate response to repeated sprints was increased more by the combination of fat adaptation and oral supplementation of sodium bicarbonate than by the sum of the responses to fat alone or bicarbonate alone. This synergism suggests that need for further studies of the interaction of fat adaptation with dietary cation-anion balance, especially under hot conditions. These results integrate harmoniously with previous findings of lower feed intake and fecal output, lower loads of heat and CO2, lower water losses in the feces and by evaporation, and less spontaneous activity and reactivity in fat adapted horses. Thus fat adaptation confers several advantages on horses and presumably other equids used for hard work, especially in the heat.

Abstract: In a 2 x 3 factorial experiment we examined the effect of exercise (no exercise/daily exercise) and paddock size (small: 150 m2, medium: 300 m2 and large: 450 m2) on the behaviour of horses. In both these treatment periods nine (three cold blood and six warm blood) adult horses were exposed to all the three paddock size treatments for 2 h daily, for 1 week in each paddock size, and the order of paddock size treatments were rotated systematically. In between turnout in paddocks the horses were all housed in tie stalls. In the non-exercise period the horses walked significantly more, they travelled a longer distance, explored more and stood more alert, than in the period with exercise. The horses stood less passively in the large paddock compared to the medium and the small paddock, and they also travelled a longer distance in the larger paddock sizes. At days with heavy rain and wind, the horses were more restless and walked significantly more than in warmer weather. In conclusion; daily exercise significantly reduced the general activity in the paddocks. Increasing the paddock size to 450 m2, increased the time spent eating grass from under the fence and decreased the time spent standing passively.

Abstract: Effects of an 18 min exercise test, on three separate occasions during a one year jump-training programme, was studied in seven horses. Determinations were carried out on venous blood for packed cell volume, haemoglobin, total protein, lactate and pyruvate, glucose, free fatty acids, insulin, glucagon, blood gases, bicarbonate, pH, aldolase, aspartate aminotransferase and alanine amino-transferase. Exercise caused a slight increase in lactate and pyruvate, total protein, aldolase, alanine aminotransferase, pO2, bicarbonate and pH. Glucose, free fatty acids and pCO2 levels decreased. Training caused no significant difference in these changes. However, during the year, increases in lactate and decreases in pH (resting levels) were observed.