Gayle L. Ecker

Gastric emptying, intestinal absorption of electrolytes and exercise performance in electrolyte‐supplemented horses

•  What is the central question of this study? The study addresses whether electrolyte supplementation of horses one hour prior to exercise improves hydration and exercise performance. •  What is the main findings and its importance? We used radiotracer methodologies to identify that 3L was the minimum amount of electrolyte supplement required to maintain hydration and replace plasma electrolytes lost by sweating. By maintaining hydration and plasma electrolyte concentrations sub‐maximal exercise duration was extended.

Time course and magnitude of changes in total body water, extracellular fluid volume, intracellular fluid volume and plasma volume during submaximal exercise and recovery in horses

The purpose of the present study was to determine the time course and magnitude of changes in extracellular and intracellular fluid volumes in relation to changes in total body water during prolonged submaximal exercise and recovery in horses. Seven horses were physically conditioned over a 2-month period and trained to trot on a treadmill. Total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). Changes in TBW were assessed from measures of body mass, and changes in PV and ECFV were calculated from changes in plasma protein concentration. Horses exercised by trotting on a treadmill for 75–120 min incurred a 4.2% decrease in TBW. During exercise, the entire decrease in TBW (mean ^ standard error: 12.8 ^ 2.0 l at end of exercise) could be attributed to the decrease in ECFV (12.0 ^ 2.4 l at end of exercise), such that there was no change in intracellular fluid volume (ICFV; 0.9 ^ 2.4 l at end of exercise). PV decreased from 22.0 ^ 0.5 l at rest to 19.8 ^ 0.3 l at end of exercise and remained depressed (18–19 l) during the first 2 h of recovery. Recovery of fluid volumes after exercise was slow, and characterized by a further transient loss of ECFV (first 30 min of recovery) and a sustained increase in ICFV (between 0.5 and 3.5 h of recovery). Recovery of fluid volumes was complete by 13 h post exercise. It is concluded that prolonged submaximal exercise in horses favours net loss of fluid from the extracellular fluid compartment.

Daily variation in plasma electrolyte and acid–base status in fasted horses over a 25 h period of rest

Measurement and interpretation of acid–base status are important in clinical practice and among racing jurisdictions to determine if horses have been administered alkalinizing substances for the purpose of enhancing performance. The present study used the physicochemical approach to characterize the daily variation in plasma electrolytes and acid–base state that occurs in horses in the absence of feeding and exercise. Jugular venous blood was sampled every 1–2 h from two groups (n 1⁄4 4 and n 1⁄4 5) of Standardbred horses over a 25 h period where food and exercise were withheld. One group of horses was studied in October and one in December. The time course and magnitude of circadian responses differed between the two groups, suggesting that subtle differences in environment may manifest in acid–base status. Significant daily variation occurred in plasma weak acid concentration ([Atot]) and strong ion difference ([SID]), [Cl ], [Kþ], [Naþ] and [lactate], which contributed to significant changes in [Hþ] and TCO2. The night-time period was associated with a mild acidosis, marked by increases in plasma [Hþ] and decreases in TCO2, compared with the morning hours. The night-time acidosis resulted from an increased plasma [Atot] due to an increased plasma protein concentration ([PP]), and a decreased [SID] due to increases in [Cl] and decreases in [Naþ]. An increased plasma [Kþ] during the night-time had a mild alkalotic effect. There were no differences in pCO2. It was concluded that many equine plasma electrolyte and acid–base parameters exhibit fluctuations in the absence of feeding and exercise, and it is likely that some of these changes are due to daily variation.