This brief review examines the athletic potential of mammals in general and the horse in particular as it relates to oxygen (O2) transport and utilization. The horse has been bred selectively for over six millennia based upon its ability to run fast. Whereas this has optimized cardiovascular and muscle function and the capacity to deliver and utilize O2, it has resulted in lung failure during intense exercise. Horses in their athletic prime are considered and attention is focused on their maximal capacities as related to O2 transport, irrespective of age per se. Following a few comments on the history of O2, this review moves from established principles of O2 transport at the integrative organ level to the microcirculation and the processes and principles that govern O2 offloading, where much remains to be discovered. Four principal questions are addressed: (1) as an athlete, what are the most outstanding physiological characteristics of the horse? (2) what anatomical and physiological capacities facilitate this superlative performance and such prodigious O2 fluxes (i.e. maximal VO2)? (3) do cardiovascular dynamics or intramuscular energetic processes limit VO2 kinetics (i.e. the speed at which VO2 increases at the onset of exercise)? VO2 kinetics determine the size of the O2 deficit and as such represent an important determinant of muscle metabolism and fatigue; and (4) what determines the efficacy of muscle microcirculatory O2 exchange?

Carbohydrate and fat are the predominant sources of energy during exercise in mammals. Carbohydrates, such as muscle glycogen and plasma glucose, and fats from adipose tissue and intramuscular triglycerides are oxidized during exercise in amounts and proportions that vary depending on the exercise intensity, level of fitness and nutritional status. In horses, muscle glycogen, and to a lesser extent plasma glucose, are oxidized in substantial amounts during low-, moderate- and high-intensity exercise. Carbohydrate availability to skeletal muscle affects exercise performance in humans, however this relationship is not well outlined in horses. Glucose supplementation by intravenous administration during exercise in horses increases duration of moderate-intensity exercise. However, the effect of glucose supplementation by ingestion of a soluble carbohydrate-rich meal prior to exercise on athletic performance has not been established in horses. Low muscle glycogen concentrations prior to exercise in horses are associated with decreased time to exhaustion at moderate- and high-intensity exercise. Nutritional interventions intended to enhance muscle glycogen resynthesis have proved less successful in horses than in other species. Replenishment of muscle glycogen after strenuous exercise in horses is not complete until 48–72 h after exercise, whereas in humans and laboratory animals it is complete by 24 h. The slower rate of muscle glycogen replenishment after exercise in horses may be related to an inherent lower ability to digest starch and other sources of glucose, a lower ability to synthesize muscle glycogen, or both. The aim of this review is to describe the present understanding of carbohydrate metabolism in the exercising horse, its implications on nutrition and athletic performance, and to contrast it with that in other species.

This study examined the effects of a rider on the angular momentum and angular velocity of the jumping horse, particularly during the flight phase. Sagittal plane video recordings were digitized of eight horses jumping a vertical fence (1 m high) under two conditions: Loose and Ridden. An experienced rider rode the horses during the Ridden condition. Using appropriate segmental inertial data for the horse and rider, angular momentum and angular velocity were calculated for the Loose and Ridden conditions. Estimates of the various rider effects on angular momentum and angular velocity were obtained by comparison of Loose and Ridden conditions and examination of the contributions of the horse and rider segments to the total angular momentum. The results showed that the rider's effect on angular momentum was significant but that the rider's segmental contribution to the angular momentum of the horse–rider system was minimal. Repeated-measures ANOVA revealed that the rider had a significant effect on the angular momentum and angular velocity of the horse during the flight phase (P<0.01). However, the rider did not have a significant effect on the transfer of angular momentum during the flight. We concluded that the rider's instruction has a greater influence on the horse's motion than the mechanical transfer between rider and horse.

Temporal stride characteristics of the canter were compared between performance-shod (PS) and light-shod (LS) Tennessee Walking Horses, which generally differ in training and shoeing methods. Four consecutive strides for ten PS and ten LS horses were filmed (30 Hz), and frame-by-frame analysis performed to determine stride duration and individual limb stance duration. Also analysed was the percentage of stride duration devoted to single, bipedal or tripedal limb support. Footfall sequence for PS was trailing hind (TrH), leading hind (LdH), trailing fore (TrF) and leading fore (LdF), whereas footfall sequence for LS horses varied, with the majority of LS performing a sequence of TrH–TrF–LdH–LdF. Stride duration was greater for PS. As a percentage of stride duration, PS demonstrated greater duration of TrF and LdF, while LS demonstrated greater LdH duration. Hind and fore single limb support, and tripedal support, were greater for LS; however, PS utilized bipedal support to a larger extent than LS. Hind or forelimb bipedal support was demonstrated only in PS, while only LS demonstrated lateral bipedal support. Thus, while both performance- and light-shod Tennessee Walking Horses perform the canter, temporal variables for this gait differ dramatically between the two groups.

The objective of this study was to apply postural sway analysis to measure balance deficits after intravenous administration of detomidine. Six healthy horses were treated intravenously with detomidine (10 μg kg−1, 20 μgkg−1) and saline in random order, with three days between treatments. Postural sway was measured immediately after administration and at 15 min intervals until 120 min had elapsed. Horses stood squarely with all four hooves on a force platform, while the location of the centre of pressure (COP) was recorded continuously for 10 s at 1000 Hz. Five 10 s recordings were analysed and average values calculated for mediolateral COP range of motion, craniocaudal COP range of motion, mean COP radius, COP area and mean COP velocity. All COP variables increased immediately after sedation, but generally returned to normal limits within 15 and 30 min of detomidine administration at 10 and 20 μg kg−1, respectively. The head was lowered for at least 90 min after administration. Balance is affected by detomidine and normal balance is regained later after a higher dose. Procedures requiring balance should not be performed within 15–30 min of detomidine administration. COP variables are a good indicator of the effect of sedation on postural sway, but head position is not.

This study aimed to produce a weight-independent algorithm for determination of body surface area (BSA; cm2) to within 5% accuracy of the directly determined value in selected horses and ponies under field conditions. Quantification of BSA in equines has applications in the fields of energy budgeting, growth, thermoregulation, conformation and drug kinetics. A simple algorithm for determining BSA to ±5% accuracy was produced for Shetland ponies, Shire horses, Welsh Mountain Section A ponies and Hanoverian mature horses and foals. The accuracy of the method was ±8% for Welsh Mountain-type ponies and Hanoverian two-year-olds. The data were produced by tiling of the shoulder region on one side of the animal with chalk and adapting a simple geometrical integrative technique. Linear anthropometric measurements were of limited use in predicting BSA in that they produced algorithms of ±5% accuracy for ponies of uniform conformation only (Welsh Mountain Section A ponies). The relevant equations were:for Arab-based breeds (Welsh Mountain-type and Section A ponies and Hanoverian horses and foals) andfor UK native breeds (Shetland ponies and Shire horses), where ‘surface area of shoulder region on one side’ was defined by the anterior margins of the supraspinatus and deep pectoral, and the posterior margin of the triceps muscles. This tiling procedure fulfilled the aim of the study and also provided quantitative information on proportional differences in areas of body regions between and within these selected breeds.

This study explored the relationship between speed-of-sound (SOS) measurements and the material properties of metacarpal bones in order to validate a device that uses linear unicortical transmission of ultrasound. SOS, ultimate tensile strength and modulus of elasticity were determined at nine experimental sites. Measurements of SOS and bone mineral density were collected at three of the nine experimental sites. Twenty-five equine metacarpal (MC3) bones were used. Micro-computerized tomography was used to validate testing protocols. SOS measurements were highly site- and horse-dependent. One or more statistically significant correlations were found with ultimate tensile strength, modulus of elasticity and bone mineral density in four of the nine experimental sites. A previously described pattern of high lateral and medial cortical stiffness and SOS was found in the mid-diaphysis that correlated with bone mineral density (r2=0.25, P<0.01) and modulus of elasticity (r2=0.14, P<0.05). SOS and ultimate tensile strength correlated strongly in the distal dorsal metacarpus (r2=0.47, P<0.001). Lateral and medial distal-level sites just above the fetlock joint had a variable amount of cancellous bone, reducing the ultimate strength of these sites. The study indicates that quantitative ultrasound is sensitive to differences in the quality of equine metacarpal bone, so this technique may be useful for monitoring adaptation to exercise and bone development.

We hypothesized that hyperlipidaemia, diabetes and diabetic dyslipidaemia increase the contractility of coronary arteries in swine, and that exercise would prevent this enhanced contractility. We further hypothesized that this enhanced contractility is associated with elevated potassium (K+) channel activity, consistent with the idea that certain disease states, as in hypertension, result in a compensatory upregulation in K+ channels. Swine were assigned to one of the following groups: control, standard chow (C; n=6); hyperlipidaemic, high-fat chow (H; n=5); diabetic, standard chow (D; n=7); diabetic, high-fat chow (‘diabetic dyslipidaemic’, DD; n=12); or exercise-trained DD (DDX; n=9). High-fat chow consisted of standard pig chow with added cholesterol (2%) and coconut oil. Endothelium-denuded segments from D, DD and DDX animals showed enhanced contractility to prostaglandin F2α (PGF2α) compared with C, while segments from H, D and DD showed enhanced contractility to endothelin-1 (ET-1) compared with C and DDX (P<0.05). The enhanced contractility was not accompanied by differences in K+ channel contribution to force reduction. There was no effect of the treatments on expression of the endothelin receptor A or endothelin receptor B. A possible mechanism for the enhanced vasoreactivity of coronary arteries of H, D and DD swine is an alteration in the signalling pathways of ET-1- and PGF2α-induced contraction. Exercise prevented the increase in contractility to ET-1, but not to PGF2α, reinforcing the concept of vasoconstrictor specificity.

Exercise is associated with an increase in the production of oxidants that may be instrumental in the development of exertional rhabdomyolysis. We speculated that participation in a long-distance sled race would alter antioxidant capacity of dogs, in conjunction with increases in indices of rhabdomyolysis. The objective was to determine the effect of participation in a long-distance sled dog race on antioxidant capacity and plasma creatine kinase (CK) activity in sled dogs. This was a prospective, longitudinal study on a convenience sample of 57 Alaskan sled dogs participating in a 1600 km sled dog race. Blood samples were collected before racing (31 dogs) and after racing (39 dogs) for measurement of plasma vitamin E concentration; CK, aspartate aminotransferase (AST) and caeruloplasmin (CER) activity; and red-blood-cell (RBC) glutathione peroxidase (GPX) and superoxide dismutase (SOD) activity. CER and GPX activities after the race were 26% and 14% lower, respectively, than before racing whereas CK and AST were 300% and 170% greater. There was no change in plasma vitamin E concentration or RBC SOD activity. We conclude that completion of a long-distance sled dog race involving prolonged and repeated submaximal exercise results in a reduction in enzymatic antioxidant activity in the blood of sled dogs.