This paper reviews the acute and chronic effects of feeding, diet composition and daily variation on equine acid–base status. The dietary cation–anion difference (DCAD) has a marked effect on blood acid–base balance in both the short term and long term. In general, diets with a low DCAD generate an acute acidosis that develops into a persistent though mild systemic, strong ion acidosis with long-term feeding. In contrast, high-DCAD diets result in a mild, persistent strong ion alkalosis characterized by elevated plasma pH, [HCO3] and total CO2 (TCO2). The acute blood acid–base responses to feeding include alterations in plasma pH and plasma concentrations of HCO3, TCO2, Cl−, Na+, K+ and protein. The forage component of the diet appears to be primarily responsible for the acute responses. There is limited research examining abrupt alterations in DCAD and the influence of daily variation on equine plasma acid–base balance. It is concluded that the composition of the diet, duration of adaptation to the diet, timing of feeding and time of day need to be considered when examining acid–base balance in horses.

High altitude acclimatization produces a suite of physiological changes that might support an improved athletic performance at low altitude and thus lead to the strategy of athletic training at high altitude. Although there is substantial literature on high altitude physiology in humans, there are few studies on horses. Our interest in the physiological responses to high altitude in equids has been driven by the concerns of how athletic performance is altered at altitude and how conditioning at altitude may improve performance subsequently at low altitude. This review serves to illustrate what is currently know about the physiological changes of horses to altitude, at rest and during exercise, and to highlight how performance is impacted both at high altitude and subsequent return to low altitude.

Chemical pollutants, for example ozone, have been demonstrated to have detrimental effects on the cardiorespiratory system in human beings. Inhalation of pollutants may therefore impact on the performance of athletes at the 2004 Athens Olympic Games. Horses will also be exposed to these pollutants contained within the large volume of air they inhale during exercise. Opportunely, the equine events will be staged outside of Athens and as a result the concentration of atmospheric chemical pollutants is likely to be lower than that experienced by many of the human athletes. The horses' housing environment should also be carefully considered as a source of pollutants, as certain bedding materials can release dust, mould spores and irritants that may induce airway inflammation. In order to achieve the highest level of performance it is essential that both horse and rider be in good health and therefore the influence of environmental pollutants on lung function should to be minimized.

Furosemide (FUR) and the equine nasal strip (NS) decrease exercise-induced pulmonary haemorrhage (EIPH) compared with control (CON) conditions in the Thoroughbred horse during near-maximal running trials. As FUR and NS have potential performance-enhancing properties, we studied Thoroughbreds running to fatigue to test the hypothesis that time-to-fatigue (TTF) would be increased, yet EIPH reduced, in FUR and NS compared with CON. Thoroughbred geldings (n=6) were run to volitional fatigue on a level treadmill (1 m s−1 increment per minute from an initial trot) every two weeks (order randomized) under CON, NS, FUR (1 mg kg−1; 4 h prior) and FUR+NS conditions. Pulmonary arterial pressure (Ppa) and pulmonary gas exchange were measured throughout exercise, while arterial blood gases were sampled at the end of each 1-min stage. EIPH severity was quantified via bronchoalveolar lavage (BAL) at 30 min post-exercise. TTF was increased for all experimental conditions (i.e. an additional 20±13, 28±8 and 40±6 s for NS, FUR and FUR+NS, respectively; P<0.05) compared with CON. Peak mean Ppa was significantly reduced (P<0.05) for FUR (93.6±6.3 mmHg) and FUR+ NS (95.4±5.1 mmHg), yet unchanged with NS (98.0±5.8 mmHg; P>0.05) compared with CON (100.5±4.9 mmHg). All three experimental conditions exhibited a significant reduction in EIPH compared with CON (64.1±36.8× 6 red blood cells (RBCs) ml−1); however, no significant difference was noted between these conditions (×106 RBCs ml−1: 29.1±16.8, 20.9±13.1 and 26.7±19.8 for NS, FUR and FUR+NS, respectively). Furthermore, no differences for either end-exercise cardiorespiratory (i.e. V˙O2 or V˙CO2) or blood-borne metabolic (i.e. blood gases, lactate or pH) variables were observed. These findings demonstrate that both FUR and NS enhance TTF and reduce EIPH to a similar degree during high-speed treadmill running to fatigue.

This study examined how horse age and gender, rider gender and individual event affected the performance of horses competing at six selected pre-novice events. Dressage accounted for 63% of penalties accumulated whilst 27.9% of penalties were from the cross-country phase and 9.1% from the show jumping phase. The data highlighted differences in the distribution of penalties between events. Male riders scored 4.5 penalties (P<0.001) less than female riders for cross-country jumping. Mares and geldings showed a very small variation (0.8 penalties) in final mean score for competition; however, stallions' mean score was 12.2 points (P<0.01) lower than mares' and 11.4 points (P<0.001) lower than geldings'. Seven-year-olds scored the fewest mean final penalty points when compared with all other age groups (P<0.001). The strongest correlations were between dressage penalty score and final placing at event, r=0.911 (P<0.01), whilst the weakest was observed between cross-country penalties and final penalty score, r=0.091 (P<0.01). It can be concluded that environmental factors exert a significant influence upon scoring at the pre-novice eventing level, both within phases of competition and over the whole competition.

The aim of this study was to investigate rider muscle activity in relation to horse movement. Electromyographic (EMG) activity of 12 upper-body muscles was recorded simultaneously with the horse's footfall timing for six riders, riding the same horse at trot. Data for five strides were analysed for each rider. Rectus abdominis, upper trapezius, middle trapezius, flexor carpi radialis, biceps brachii, triceps brachii and middle deltoid muscles had constant patterns with two peaks occurring in the same phase of the stride in all riders. Peak EMG values in the upper trapezius and middle trapezius occurred in early stance, and were considered to stabilize the rider's neck and scapula during impact of the diagonal limbs. The rectus abdominis showed peak EMG activity in mid-stance to stabilize the trunk and enable the rider to follow the horse's movement by swinging the pelvis forward as the horse's body reversed direction from downward to upward motion. The triceps brachii, which was active during late stance, and the biceps brachii, which was activated early in stance, stabilized the rider's hands and maintained contact with the bit. Teres major, extensor carpi ulnaris and serratus anterior muscles had a small range of activity (33, 26 and 37%, respectively), consistent with tonic activation or were inactive, suggesting that their function may be related to general postural control.

The present study tested the hypothesis that multi-frequency bioelectrical impedance analysis (MFBIA) can be used to provide reasonable estimates of body mass, total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) at rest, during exercise-induced dehydration and subsequent recovery. Seven exercise-conditioned horses were administered indicators for measurement of resting TBW, ECFV and PV. MFBIA measurements at 24 frequencies between 5 and 280 kHz were obtained at rest, during prolonged submaximal exercise and for up to 13 h of recovery with food and water provided. Impedance–frequency response curves were described by a double-exponential decay equation from which coefficients were used, together with height and length, to generate predictive equations for estimating body mass, TBW, ECFV and PV. Predictive equations for body mass, ECFV and PV provided reasonable estimates of the parameter at rest and during exercise and recovery that were within 6% of absolute values determined using indicators. Despite the inherent error in estimating absolute volumes, the technique allowed accurate (within 1%) determination of the change in compartment volumes within individual horses over time. The number of frequencies at which impedance was measured could be reduced to seven without sacrificing the accuracy of the impedance–frequency relationships or the predictive equations – this enabled a 70% reduction in data-acquisition time (to ∼35 s) for each MFBIA measurement series. It is concluded that MFBIA can be used in individual horses to track changes in compartmental hydration status resulting from dehydration and rehydration.

This study investigated the effect of training and exercise intensity on blood antioxidant markers in six healthy Standardbred horses. Markers studied were uric acid (UA), ascorbic acid (AA), α-tocopherol, vitamin A (Vit A), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione – reduced (GSH) and oxidized (GSSG), glutathione redox ratio (GRR), copper (Cu), zinc (Zn) and selenium (Se). The horses performed a standardized exercise test (SET) when they were untrained (T0), after 4 weeks of light training (T4) and after 8 weeks of interval training (T12). Forty-eight hours after SET T4 and SET T12, a SET with run up to fatigue (TTF4 and TTF12) was performed. Maximal oxygen consumption (V˙O2max) was determined within 3–5 days after TTF4 and TTF12. At each test (SET T(i) and TTF(i)), venous blood was sampled at rest (R), peak-exercise (Emax), 15 (E15) and 60 (E60) min after the test. UA, AA and GRR were increased significantly by the exercise, whereas GSH and Vit A were decreased significantly (P<0.05). Training-related increases (T0 vs. T4 vs. T12) were observed for UA, SOD, GPx and Se, whereas GSH, α-tocopherol and Zn decreased (P<0.05). Exercise intensity (TTF(i) vs. T(i)) increased UA and AA significantly and decreased GSH significantly (P<0.05). A significant correlation between ΔSOD and ΔV˙O2max (r=0.86, p<0.05) determined at SET T4 and SET T12 was found. Taken together, these results indicate that training and exercise intensity significantly influence blood antioxidant markers in healthy Standardbred horses.