Four mathematical approaches are proposed to determine optimal ranges of nutrients for specified purposes. For exercise, the diet must provide optimal mixtures of fuels, also optimal amounts of nutrients conducive to a sound structure, a desired power/weight ratio, a water-electrolyte system that resists dehydration and buffers hydrogen ions, a tolerance to the cumulative stress of repetitive competition and tractable attitude. The nutritional strategy of carbohydrate loading risks a variety of abnormalities in dogs and horses. An alternative strategy of fat adaptation (the combination of fat feeding and training) was found to improve aerobic performance in dogs and horses and to spare glycogen utilization and reduce lactate accumulation. Surprisingly, improved anaerobic performance has also been confirmed in fat-adapted horses that have been sprint trained. Fat adaptation increased the blood lactate responses to incremental tests and repeated sprints. Blood lactate accumulation during repeated sprints was affected synergistically by the combination of fat adaptation and sodium bicarbonate supplementation. Fat adaptation in horses appears to facilitate metabolic regulation to achieve power needs, with glycolysis decreasing during aerobic work but increasing during anaerobic work and with blood lactate changes following accordingly. Interactions between fat adaptation and dietary cation-anion balance need further investigation.

Rectal temperature (Tre) is often used to adjust measurements of blood gases, but these adjusted measurements may not approximate temperatures during intense exercise at main sites of gas exchange: muscle and lung. To evaluate differences in blood gases between sites, temperatures (T) were measured with thermocouples in the rectum (re), in mixed venous blood (v), in gluteal muscle (mu), and on the skin (sk) in seven Arabian horses as they underwent an incremental exercise test on a treadmill. Blood samples were drawn from the carotid artery and pulmonary artery (mixed venous) 30 s before each increase in speed and during recovery. Blood gases and pH were measured at 37 degreesC, and all variables were adjusted to Tre, Tv, and Tmu. Adjusted variables during exercise and recovery were significantly different from each other at the three sites. Linear and polynomial equations described the time course of venous temperature and from Tre and Tsk during exercise and from Tsk during recovery. Interpretation of changes in muscle metabolism and gas exchanges based on blood-gas measurements is improved if they are adjusted appropriately to Tmu or Tv, which may be predicted from Tsk in addition to Tre during strenuous exercise and from Tsk during recovery.

Seven Arabian horses performed a standard incremental exercise test on a high-speed treadmill at 6% slope then were randomly assigned to two diets, a control diet of ground hay and concentrates and a similar diet with 10% added fat (by weight). Horses were sprint-trained 4 d/wk, and two additional exercise tests were performed at 5-wk intervals. Heart rates and rectal temperatures were monitored and venous blood samples were collected at rest and at each speed increment. Whole blood was analyzed for glucose, lactate, and hemoglobin concentrations, and plasma was analyzed for pH, pCO2, albumin, total protein, and sodium, potassium, and chloride concentrations. Bicarbonate concentration ([HCO3-]) and strong ion difference ([SID]) were calculated, and total weak acid ([Atot]) was estimated from total protein. During exercise, there were increases in plasma sodium and potassium concentrations (P < .001), whole blood lactate and glucose (P < .001), and hemoglobin concentrations (P < .01). There were decreases in plasma pH, [HCO3-], and chloride concentrations (P < .001). The decrease in plasma pH was associated with changes in [SID] and [Atot] that combined to offset a decrease in pCO2. After sprint training, heart rates at rest and during submaximal exercise were decreased (P < .01), whereas heart rates at the end of exercise were increased (P < .05). Sprint training also increased workrate and estimated oxygen consumption at a heart rate of 200 beats/min (P < .001). Training increased the duration of exercise and the speed attained at the end of exercise (P < .05). Training increased the blood hemoglobin response to exercise and decreased the pCO2 response (P < .01). There were diet x training interactions for pH, pCO2, and [SID] (P < .05). Horses consuming the high-fat diet had higher blood glucose during both standard exercise tests and higher lactate concentrations at fatigue (P < .05) during the last test. Fat adaptation involving sprint training of horses may influence glucolysis at the level of pyruvate during an incremental exercise test.

Summary Seven horses performed six, 1 min sprints separated by 4 min intervals at a walk, followed by a 30 min recovery period. To evaluate changes in blood gases and strong ions, blood samples were taken from the carotid artery (A) and the right heart (mixed venous, V) at rest, after a submaximal warm‐up, during the last 15 s of sprints 5 and 6 and at 5 and 30 min of recovery. At both arterial and venous sites, plasma [H+], PCO2, PO2, albumin ([Alb]), strong ion concentrations ([Na+], [K+], [Cl−]), blood lactate ([Lac]) and haemoglobin concentrations ([Hb]) were measured. Strong ion difference ([SID]), bicarbonate concentration ([HCO3−]) and total weak acid ([Atot]) were calculated. Between sites (A vs. V) there were differences in [H+], PCO2, PO2, [HCO3−], [Cl−], [SID], [Na+], [K+] and [Lac−]. Arterial PO2 remained constant during exercise, was increased at 5 min recovery and returned to the resting level by 30 min recovery. The PvO2 decreased during exercise before returning to resting levels at 5 min of recovery. During exercise, [Cl−] increased at A and decreased at V, which is consistent with the chloride shift. The [H+], PCO2 and [HCO3−] decreased at A and increased at V. During exercise, [Na+], [K+] and [Lac] increased at both sites, with [Na+]V, [K+]V and [Lac−]A increasing to a greater extent. Plasma [SID]A decreased due to a greater increase in [Lac−]A compared to other strong ions and [SID]V increased due to increased [Na+]V and [K+]V and decreased [Cl−]V. Plasma [Alb] and blood [Hb] increased with exercise, with no site differences. Plasma [H+] increased at V and decreased at A before returning to pre‐exercise values at 30 min recovery. These changes reflected the patterns of change in PCO2, but not [SID]. In turn, the decrease in PaCO2 was probably associated with hyperventilation that maintained the PaO2 at a constant level during repeated sprints. Results show that SID, [Atot] and PCO2 have different effects on plasma [H+] and [HCO3−] at sites A and V and that the chloride shift is evident in the exercising horse.

Lactate breakpoints can be determined for horses, using blood lactate concentration versus speed curves generated during submaximal IET and may be useful for assessing fitness and monitoring training programs in equine athletes.