Effects of exercise, furosemide, blood depletion, and reinfusion on body fluid compartment volumes in horses.

High pulmonary blood pressure contributes to exercise-induced pulmonary hemorrhage. The objective of this study was to use bioimpedance spectroscopy to assess body fluid compartment volumes under 3 conditions in 6 racehorses: i) Pre- and post-supramaximal treadmill exercise (control); ii) Exercise 4 hours after furosemide (0.5 mg/kg body weight, IV); iii) Exercise, removal of ~14 L of blood and subsequent reinfusion of the blood. Statistical analysis used linear mixed effects models. Body compartment volumes did not change during the control runs. Total body water (TBW) (P = 0.007, P = 0.007), extracellular fluid (ECF) (P = 0.003, P = 0.003), and intracellular fluid (ICF) volumes (P = 0.04, P = 0.04) decreased pre- and post-exercise following furosemide administration. The ICF trended to decrease (P = 0.07) after slow removal of blood. Blood reinfusion increased TBW (P = 0.02, P = 0.02) and ICF (P = 0.005, P = 0.005) pre- and post-exercise.

Effets de l'exercice, du furosémide, de la diminution sanguine et de la ré-infusion sur les volumes des liquides corporels compartimentés chez les chevaux. Une pression sanguine pulmonaire élevée contribue à des hémorragies pulmonaires induites par l'exercice. L'objectif de la présente étude était d'utiliser la spectroscopie à bio-impédance pour évaluer les volumes des liquides corporels compartimentés sous trois conditions chez six chevaux de course : i) Pré- et post-supramaximal exercice au tapis roulant (témoin); ii) Exercice 4 h après administration de furosémide (0,5 mg/kg de poids corporel, IV); iii) Exercice, retrait d'environ 14 L de sang et ré-infusion subséquente du sang. Les analyses statistiques utilisaient des modèles linéaires à effets mixtes. Les volumes des compartiments corporels n'ont pas changé durant les essais témoins. Les volumes de la quantité totale d'eau corporelle (TBW) (P = 0,007, P = 0,007), de liquide extracellulaire (ECF) (P = 0,003, P = 0,003) et liquide intracellulaire (ICF) (P = 0,04, P = 0,04) ont diminué pré- et post-exercice à la suite de l'administration de furosémide. L'ICF avait tendance à diminuer (P = 0,07) à la suite du lent retrait de sang. La ré-infusion de sang augmenta la TBW (P = 0,02, P = 0,02) et l'ICF (P = 0,005, P = 0,005) pré- et post-exercice.(Traduit par Dr Serge Messier).

Conditioning equine athletes on water treadmills significantly improves peak oxygen consumption.

Equine water treadmills (WT) were initially designed for rehabilitation of musculoskeletal injuries, but are also commonly used for conditioning sport horses, however the effects are not well documented. The purpose of this study was to test the effect of an 18-day WT conditioning programme on peak oxygen consumption (V̇O2peak). Nine unfit Thoroughbreds were used in a randomised controlled trial. Six horses worked daily for 18 days in stifle-height water (WT group), while 3 control horses worked without water (dry treadmill group (DT)). Preconditioning and postconditioning maximal exercise racetrack tests (800 m) were performed using a portable ergospirometry system. Measured outcomes were V̇O2, tidal volume, minute ventilation, breathing frequency, heart rate, blood lactate and instantaneous and average speed. The workload as assessed by V̇O2 was 21.7 per cent of preconditioning V̇O2peak values for WT horses. V̇O2peak on the racetrack increased by 16.1 per cent from preconditioning to postconditioning in the WT horses (P=0.03), but did not change in the DT horses. Therefore, exercising horses in high water heights may improve conditioning.

Effect of different protocols on the mitigation of exercise-induced pulmonary hemorrhage in horses when administered 24 hours before strenuous exercise.

BACKGROUND: Public pressure exists in the United States to eliminate race-day furosemide administration despite its efficacy in decreasing the severity of equine exercise pulmonary hemorrhage (EIPH). No effective alternative prophylaxis strategies have been identified. OBJECTIVE: To investigate alternative protocols to race-day furosemide that might mitigate EIPH. ANIMALS: Seven fit Thoroughbreds with recent EIPH. METHODS: Double-blinded placebo-controlled Latin square crossover using a treadmill followed by a blinded placebo-controlled crossover study at a racetrack. First, horses exercised supramaximally to fatigue 24 hours after initiating 5 EIPH prophylaxis protocols: 0.5 and 1.0 mg/kg furosemide IV 24 hours pre-exercise with and without controlled access to water, and 24 hour controlled access to water. Effects were compared to those measured after giving a placebo 24 hours pre-exercise, and 0.5 mg/kg furosemide IV 4 hours pre-exercise. Bronchoalveolar lavage (BAL) erythrocyte count was determined 45-60 minutes postexercise after endoscopy to assign an EIPH score. Data were analyzed using linear mixed effects models. The most promising protocol from the treadmill study was further evaluated in 6 horses using endoscopy and BAL after 1100 m simulated races. RESULTS: Intravenous furosemide (0.5 mg/kg) administered 24 hours pre-exercise combined with controlled access to water decreased the severity of EIPH on the treadmill and at the racetrack. CONCLUSION AND CLINICAL IMPORTANCE: Administering 0.5 mg/kg furosemide 24 hours pre-racing combined with controlling water intake may be a strategy to replace race-day furosemide administration for the management of EIPH. A larger study is indicated to further evaluate whether this protocol significantly mitigates EIPH severity.

Assessment of two methods to determine the relative contributions of the aerobic and anaerobic energy systems in racehorses.

A prospective, randomized, controlled study was designed to determine relative aerobic and anaerobic (lactic and alactic) contributions at supramaximal exercise intensities using two different methods. Thoroughbred racehorses (n = 5) performed a maximal rate of oxygen consumption (V̇o2max) test and three supramaximal treadmill runs (105, 115, and 125% V̇o2max). Blood lactate concentration (BL) was measured at rest, every 15 s during runs, and 2, 5, 10, 20, 30, 40, 50, and 60 min postexercise. In method 1, oxygen demand was calculated for each supramaximal intensity based on the V̇o2max test, and relative aerobic and anaerobic contributions were calculated from measured V̇o2 and the accumulated oxygen deficit. In method 2, aerobic contribution was calculated using the trapezoidal method to determine V̇o2 during exercise. A monoexponential model was fitted to the postexercise V̇o2 curve. Alactic contribution was calculated using the coefficients of this model. Lactate anaerobic contribution was calculated by multiplying the peak to resting change in BL by 3. Linear mixed-effects models were used to examine the effects of exercise intensity and method (as fixed effects) on measured outcomes (P ≤ 0.05). Relative aerobic and anaerobic contributions were not different between methods (P = 0.20). Horses' mean contributions were 81.4, 77.6, and 72.5% (aerobic), and 18.5, 22.3, and 27.4% (anaerobic) at 105, 115, and 125% V̇o2max, respectively. Individual alactic anaerobic energy was not different between supramaximal exercise intensities (P = 0.43) and was negligible, contributing a mean of 0.11% of the total energy. Relative energy contributions can be calculated using measured V̇o2 and BL in situations where the exercise intensity is unknown. Understanding relative metabolic demands could help develop tailored training programs. NEW & NOTEWORTHY Relative energy contributions of horses can be calculated using measured V̇o2 and BL in situations where the exercise intensity is unknown. Horses' mean contributions were 81.4, 77.6, and 72.5% (aerobic), and 18.5, 22.3, and 27.4% (anaerobic) at 105, 115, and 125% of V̇o2max, respectively. Individual alactic capacity was unaltered between supramaximal exercise intensities and accounted for a mean contribution of 0.11% of energy use.

Workload of horses on a water treadmill: effect of speed and water height on oxygen consumption and cardiorespiratory parameters.

BACKGROUND: Despite the use of water treadmills (WT) in conditioning horses, the intensity of WT exercise has not been well documented. The workload on a WT is a function of water height and treadmill speed. Therefore, the purpose of this study was to determine the effects of these factors on workload during WT exercise. Fifteen client-owned Quarter Horses were used in a randomized, controlled study. Three belt speeds and three water heights (mid cannon, carpus and stifle), along with the control condition (dry treadmill, all three speeds), were tested. Measured outcomes were oxygen consumption (V̇O2), ventilation (respiratory frequency, tidal volume (VT)), heart rate (HR), and blood lactate. An ergospirometry system was used to measure V̇O2 and ventilation. Linear mixed effects models were used to examine the effects of presence or absence of water, water height and speed (as fixed effects) on measured outcomes. RESULTS: Water height and its interaction with speed had a significant effect on V̇O2, VT and HR, all peaking at the highest water level and speed (stifle at 1.39 m/s, median V̇O2 = 16.70 ml/(kg.min), VT = 6 L, HR = 69 bpm). Respiratory frequency peaked with water at the carpus at 1.39 m/s (median 49 breaths/min). For a given water height, the small increments in speed did not affect the measured outcomes. Post-exercise blood lactate concentration did not change. CONCLUSIONS: Varying water height and speed affects the workload associated with WT exercise. The conditions utilized in this study were associated with low intensity exercise. Water height had a greater impact on exercise intensity than speed.