Electrolyte and glycerol supplementation improve water intake by horses performing a simulated 60 km endurance ride

The effects of feeding sodium chloride pellets on the gastric mucosa, acid-base, and mineral status in exercising horses

BACKGROUND

Electrolyte supplementation may be a risk factor for gastric mucosal lesions, but relevant evidence is limited in horses.

HYPOTHESIS

Investigate the effects of PO sodium chloride (NaCl) supplementation on the gastric mucosa of exercising horses. We hypothesized that NaCl supplementation would neither cause nor exacerbate existing gastric mucosal damage.

ANIMALS

Fifteen 3-year-old healthy Warmblood stallions from a stud farm.

METHODS

Placebo-controlled study with a crossover design. Horses were fed either a NaCl pellet at a dosage adequate to replace the electrolyte losses in 10 L sweat or a placebo for 19 days with a washout period of 14 days between treatments. The gastric mucosa was evaluated by gastroscopy before and after treatment. Blood samples were collected for evaluation of acid-base status, packed cell volume (PCV), and total protein, creatinine and blood urea nitrogen concentrations. Urine was collected, and urine specific gravity, electrolyte, creatinine, and urea concentrations were measured.

RESULTS

The initial prevalence of gastric mucosal lesions was 85%. Sodium chloride pellets did not adversely affect the gastric mucosa and treatment did not significantly alter the hematologic and serum biochemical variables. Urine creatinine concentrations significantly decreased and urinary sodium concentrations significantly increased after supplementation with NaCl pellets. Water intake did not significantly differ between treatments.

CONCLUSIONS AND CLINICAL IMPORTANCE

Daily NaCl pellet supplementation is a palatable and safe way to replace electrolyte losses from sweating in exercising horses and has no negative effects on the gastric mucosa.

Oral Electrolyte and Water Supplementation in Horses

Horses that sweat for prolonged periods lose considerable amounts of water and electrolytes. Maintenance of hydration and prevention of dehydration requires that water and electrolytes are replaced. Dehydration is common in equine disciplines and can be avoided, thus promoting equine wellness, improved performance and enhanced horse and rider safety. Significant dehydration occurs through exercise or transport lasting one hour or more. Oral electrolyte supplementation is an effective strategy to replace water and electrolytes lost through sweating. The stomach and small intestine serve as a reservoir for uptake of water and electrolytes consumed 1 to 2 h prior to exercise and transport. The small intestine is the primary site of very rapid absorption of ions and water. Water and ions absorbed in the small intestine are taken up by muscles, and also transported via the blood to the skin where they serve to replace or augment the losses of water and ions in the body. Effective electrolyte supplements are designed to replace the proportions of ions lost through sweating; failure to do so can result in electrolyte imbalance. Adequate water must be consumed with electrolytes so as to maintain solution osmolality less than that of body fluids in order to promote gastric emptying and intestinal absorption. The electrolyte supplement should taste good, and horses should be trained to drink the solution voluntarily prior to and during transport, and prior to and after exercise.

Pre-loading large volume oral electrolytes: tracing fluid and ion fluxes in horses during rest, exercise and recovery

KEY POINTS

Exercise results in rapid and large extracellular to intracellular fluid shifts, as well as significant sweating losses of water and ions. It is unknown whether ions within oral electrolyte supplements are taken up by muscle (and other soft tissues) and whether oral supplementation can effectively offset sweating losses. Pre-loading with 8 L of a balanced hypotonic electrolyte supplement attenuated extracellular fluid losses, increased exercise duration and increased sweating fluid and ion losses during submaximal exercise. Supplemented electrolytes appear in skeletal muscle within 1 h after administration. Electrolyte supplementation increased exercise performance, improved maintenance of extracellular fluid volumes, and attenuated body fluid losses while maintaining sweating rates.

ABSTRACT

This study used radioactive sodium (24 Na) and potassium (42 K) in a balanced, hypotonic electrolyte supplement to trace their appearance in skeletal muscle, and also quantified extracellular and whole-body fluid and ion changes during electrolyte supplementation, exercise and recovery. In a randomized crossover design, 1 h after administration of 1 to 3 L of water or electrolyte supplement with 24 Na, horses were exercised at 35% VO2max to voluntary fatigue or, after administration of 8 L of water or electrolyte supplement with 42 K were exercised at 50% peak VO2 for 45 min (n = 4 in each trial). Pre-exercise electrolyte supplementation was associated with decreased loss of fluid and electrolytes from the extracellular fluid compartments during exercise and recovery compared with water alone. The improved fluid and ion balance during prolonged exercise was associated with increased exercise duration, despite continuing sweating losses of fluid and ions. Nasogastric administration of radiotracer 24 Na+ and 42 K+ showed rapid absorption into the blood with plasma levels peaking 45 min after administration, followed by distribution into the extracellular space and intracellular fluid of muscle within 1 h. Following exercise, virtually all Na+ remained within the extracellular compartment, while the majority of K+ underwent intracellular uptake by 2 h of recovery. It is concluded that pre-loading with a large volume, balanced electrolyte supplement helps maintain whole-body fluid and ion balance and support muscle function during periods of prolonged sweat ion losses.

Metabolic changes in four beat gaited horses after field marcha simulation

REASONS FOR PERFORMING STUDY

Mangalarga-Marchador is a popular 4-gaited Brazilian horse breed; however, there is little information about their metabolic and physiological response to exercise.

OBJECTIVES

To measure physiological and metabolic responses of the Mangalarga-Marchador to a simulated marcha field test and to compare these responses between 2 types of marcha gaits (picada and batida).

METHODS

Thirteen horses were used in the study and randomly assigned to either the picada or batida gait for the simulated marcha field test (speed ∼ 3.2 m/s; 30 min; load ∼ 80 kg).

MEASUREMENTS

Included body composition, heart rate (HR), respiratory rate (RR), glucose (GLUC), lactate (LACT), packed cell volume (PCV), total plasma protein (TPP), albumin, urea, creatinine, total and HDL cholesterol, triglycerides, creatine kinase, alanine, glutamate and glutamine (GLN). Measurements were obtained pretest (control/fasting), immediately after simulation (T(0)), and 15 (T(15)), 30 (T(30)) and 240 (T(240)) min after the simulation. Lactate (LACT) was measured at T(0), T(15) and T(30). Data were analysed using ANOVA, Tukey's test and t tests with significance set at P < 0.05.

RESULTS

Significant acute changes were observed in HR, RR, [GLUC], [LACT], [TPP], PCV and [GLN] (P<0.05) relative to control. Heart rate fell below 60 beats/min at T(15) and RR recovered to pretest values by T(240). Significant increases in [GLUC], [LACT], PCV and [TPP] and a decrease in [GLN] were observed at T(0). Treatment and interaction effects were also observed between marcha types and time of sampling for HR, RF, PCV, and [LACT] (P < 0.05). These parameters were large in picada.

CONCLUSION

The simulation of field-test produced changes in some physiological and blood parameters in marcha horses, with some degree of dehydration during recovery period. Also, it was demonstrated that picada horses spend more energy when compared with batida horses at the the same speed.

POTENTIAL RELEVANCE

Batida horses spend less energy when compared with picada horses, which will need special attention in their training and nutritional management.

Effects of oral electrolyte supplementation on endurance horses competing in 80 km rides

REASONS FOR PERFORMING STUDY

There is no evidence that use of oral electrolyte pastes enhances performance in competing endurance horses.

OBJECTIVE

To ascertain whether oral administration of a high dose (HD) of sodium chloride (NaCl) and potassium chloride (KCl) to endurance horses would differentially increase water intake, attenuate bodyweight (bwt) loss and improve performance when compared to a low dose (LD).

METHODS

A randomised, blinded, crossover study was conducted on 8 horses participating in two 80 km rides (same course, 28 days apart). Thirty minutes before and at 40 km of the first ride 4, horses received orally 02 g NaCl/kg bwt and 0.07 g KCl/kg bwt. The other 4 received 0.07 g NaCl/kg bwt and 0.02 g KCl/kg bwt. Horses received the alternate treatment in the second ride. Data were analysed with 2-way ANOVA for repeated measures (P<0.05).

RESULTS

Estimated water intake was significantly greater with HD both at the 40 km mark and as total water intake; however, differences in bwt loss and speed between HD and LD were not found. Treatment significantly affected serum Na+, Cl-, HCO3, pH and water intake, but not serum K+ or bwt. Serum Na+ and Cl- were significantly higher at 80 km when horses received HD, but no differences were found in early recovery. Venous HCO3- and pH were significantly lower throughout the ride and in early recovery when horses received HD.

CONCLUSIONS AND POTENTIAL RELEVANCE

Other than enhancing water intake, supplementing endurance horses with high doses of NaCI and KCl did not provide any detectable competitive advantage in 80 km rides. Further, the elevated serum electrolyte concentrations induced with HD might not be appropriate for endurance horses.

Does usefulness of potassium supplementation depend on speed?

REASONS FOR PERFORMING STUDY

Electrolyte mixtures given to counter sweat loss usually contain abundant potassium. However, increases in plasma [K+] occur with exercise and supplementation may further increase plasma levels, potentially increasing the risk of neuromuscular hyperexcitability and development of adverse clinical sequellae. This proposition requires study.

OBJECTIVES

To compare effects of a K-rich electrolyte supplement (EM+K) to a K-free one (EM-K) on plasma [K+], [Ca++] and acid-base status during an endurance incremental exercise test on the treadmill.

METHODS

The test consisted of 3 bouts (simulating loops in an endurance race) of 12 km performed at 6, then 7, then 8 m/sec with 25 min rest stops (S1, S2) between loops on 13 endurance trained Arabian horses (7 EM-K, 6 EM+K). Electrolytes were supplied orally 60 mins before exercise (Pre) and at each stop. Blood samples were taken before exercise and during exercise, each S and 120 mins of recovery (R). Blood was analysed for pH, PCO2, packed cell volume (PCV), plasma [Na+], [K+], [Cl-], [Ca++], glucose, and lactate [La-]; plasma [H+] and osmolality (osm) were calculated. The dietary cation anion difference (DCAD) was calculated to be -27 meq/dose EM-K and 109 meq in EM+K, respectively.

RESULTS

Plasma [H+] decreased during the 6 and 7 m/sec loops, increased during the 8 m/sec loop, and returned to Pre at S1, S2 and R. Plasma [K+] was higher at 8 m/sec and plasma [Ca++] was overall lower in the EM+K group compared to EM-K. Other findings included higher overall PCV, overall glucose, and [La-] during the 8 m/sec loop (P<0.040) in EM+K compared to EM-K horses.

CONCLUSIONS

EM+K supplementation leads to higher plasma [K+] increasing the risk of neuromuscular hyperexcitability during exercise. Acute effects of a lower DCAD in EM-K may have led to higher plasma [Ca++]. Potassium-rich electrolytes may have triggered the release of epinephrine, contributing to higher PCV, glucose release and increased lactate production.

POTENTIAL RELEVANCE

Lower plasma [K+] and higher plasma [Ca++] with EM-K supplementation may help reduce the risk of conditions associated with neuromuscular hyperexcitability occurring especially during higher speeds in endurance races.

Enteral fluid therapy in large animals

Enteral fluids administered alone, or in conjunction with intravenous fluids, are reported to be useful for the treatment of dehydration and electrolyte loss associated with diarrhoea in a number of species, following exercise in horses and for feed impaction of the large intestine of horses. Enteral fluids are suitable for treatment of mild to moderately dehydrated patients with some intact intestinal epithelium and motile small intestine. In patients that will drink voluntarily or tolerate nasal intubation the use of enteral fluids may avoid the complications associated with intravenous fluid administration. However the labour costs associated with repeated nasal intubation in intensively managed patients requiring large volumes of fluids may make the use of enteral fluids less economical than intravenous fluid administration. Enteral fluid use alone is contraindicated in patients that are severely dehydrated and/or in hypovolaemic shock, however, if used in conjunction with intravenous fluids, the effects of villous atrophy and malnutrition may be ameliorated and the duration of hospitalisation shortened. There is a variety of commercially available enteral fluids available to veterinary practitioners. While the key components of these fluids are sodium, chloride and carbohydrates, the amounts of ions and other ingredients such as potassium, alkalising agents, amino acids and shortchain fatty acids may vary. The species of the animal, the underlying condition, and the constituents of the fluid, should influence the choice of an enteral fluid.

Effects of oral potassium supplementation on acid-base status and plasma ion concentrations of horses during endurance exercise

OBJECTIVE

To compare effects of oral supplementation with an experimental potassium-free sodium-abundant electrolyte mixture (EM-K) with that of oral supplementation with commercial potassium-rich mixtures (EM+K) on acid-base status and plasma ion concentrations in horses during an 80-km endurance ride.

ANIMALS

46 healthy horses.

PROCEDURE

Blood samples were collected before the ride; at 21-, 37-, 56-, and 80-km inspection points; and during recovery (ie, 30-minute period after the ride). Consumed electrolytes were recorded. Blood was analyzed for pH, PvCO2, and Hct, and plasma was analyzed for Na+, K+, Cl-, Ca2+, Mg2+, lactate, albumin, phosphate, and total protein concentrations. Plasma concentrations of H+ and HCO3-, the strong ion difference (SID), and osmolarity were calculated.

RESULTS

34 (17 EM-K and 17 EM+K treated) horses finished the ride. Potassium intake was 33 g less and Na+ intake was 36 g greater for EM-K-treated horses, compared with EM+K-treated horses. With increasing distance, plasma osmolarity; H+, Na+, K+, Mg2+, phosphate, lactate, total protein, and albumin concentrations; and PvCO2 and Hct were increased in all horses. Plasma HCO3-, Ca2+, and Cl- concentrations were decreased. Plasma H+ concentration was significantly lower in EM-K-treated horses, compared with EM+K-treated horses. Plasma K+ concentrations at the 80-km inspection point and during recovery were significantly less in EM-K-treated horses, compared with EM+K-treated horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Increases in plasma H+ and K+ concentrations in this endurance ride were moderate and unlikely to contribute to signs of muscle fatigue and hyperexcitability in horses.

Rehydration fluid temperature affects voluntary drinking in horses dehydrated by furosemide administration and endurance exercise

To determine whether temperature of rehydration fluid influences voluntary rehydration by horses, six 2-3-year-old horses were dehydrated (4-5% body weight loss) by a combination of furosemide administration and 30 km of treadmill exercise. For the initial 5 min following exercise, horses were offered a 0.9% NaCl solution at 10, 20, or 30 degrees C. Subsequently, after washing and cooling out, voluntary intake of water at 10, 20, or 30 degrees C from 20 to 60 min after exercise was measured. Fluid intake (FI) during the first 5 min of recovery was 9.8+/-2.5,12.3+/-2.1 and 9.7+/-2.0L (p>0.05) for saline at 10, 20, and 30 degrees C, respectively. Although not a significant finding, horses offered 0.9% NaCl at 20 degrees C tended to take fewer (p=0.07), longer drinks than when saline at either 10 or 30 degrees C was offered. Between 20 and 60 min of recovery, intake of water at 20 degrees C (7.7+/-0.8L) and 30 degrees C (6.6+/-1.2L) was greater (p<0.05) than that at 10 degrees C (4.9+/-0.5L). Thus, total FI was 14.7+/-2.5,19.9+/-2.5, and 16.3+/-2.4L for rehydration fluids at 10, 20, and 30 degrees C, respectively (p<0.05, value for 20 degrees C water greater than that for 10 degrees C water). Although the amount of metabolic heat transferred to the initial saline drink was correlated with the decrease in core temperature during the initial 5 min of recovery, heat transfer to ingested fluid was most likely responsible for the dissipation of, at most, 5% of the heat generated during endurance exercise. In conclusion, following exercise these dehydrated-normothermic horses voluntary drank the greatest amount of fluid at near ambient (20 degrees C) temperature. Although not determined in this study, greater satiation of thirst by oropharyngeal cooling may have contributed to lesser intake of colder (10 degrees C) fluid.

Effect of varying initial drink volume on rehydration of horses

Body mass (BM), water intake (WI), and plasma osmolality (P(osm)) and electrolyte concentrations were measured in six 2-year-old Arabian horses provided either 4 l, 8 l, or an unlimited amount of water (UW) for drinking during the initial 5 min of recovery from 45-km of treadmill exercise. After weighing, horses were placed in a stall and further WI between 20 and 60 min of recovery was measured. During exercise, horses lost 3.3+/-0.3%, 3.2+/-0.1%, and 3.3+/-0.2% (P>.05) of BM and P(osm) increased by 7.2+/-0.5, 7.9+/-0.8, and 7.7+/-0.5 mOsm/kg (P>.05) for 4 l, 8 l, and UW, respectively. WI during the first 5 min of recovery was 4.0+/-0.0, 8.0+/-0.0, and 9.0+/-1.3 l and was accompanied by 2.4+/-0.4, 5.8+/-0.9, and 6.1+/-0.7 mOsm/kg decreases (P<.05) in P(osm) for 4 l, 8 l, and UW, respectively. Between 20 and 60 min of recovery, WI was 6.2+/-1.5, 1.2+/-0.6, and 1.0+/-0.7 l (P<.05) for 4 l, 8 l, and UW, respectively. Thus, total WI was 10.2+/-1.5, 9.2+/-0.6, and 10.0+/-1.1 l (P>.05) for 4 l, 8 l, and UW, respectively. After 60 min of recovery, persisting BM loss was 1.3+/-0.5%, 1.1+/-0.2%, and 1.0+/-0.2% (P>.05) for 4 l, 8 l, and UW, respectively and P(osm) had returned to pre-exercise values for all treatments. In conclusion, limiting the volume of water initially provided to horses dehydrated by endurance exercise had no significant effect on total WI during the initial 60 min of recovery; however, persisting BM loss was observed with all treatments. Further, following exercise-induced dehydration, the primary stimulus of thirst was an increase in plasma tonicity rather than hypovolemia.

Equine endurance exercise alters serum branched-chain amino acid and alanine concentrations

Six 2-year-old Arabian horses were used to determine whether 60 km prolonged endurance exercise (approximately 4 h) alters amino acid concentrations in serum and muscle, and the time required for serum amino acid concentrations to return to basal resting values. Blood and muscle samples were collected throughout exercise and during a 3 day recovery period. Isoleucine concentration in muscle tended to increase and leucine and valine did not change due to exercise. Serum alanine concentrations did not increase immediately after exercise, but increased at 24, 48 and 72 h postexercise. Serum isoleucine, leucine, and valine concentrations decreased after exercise and time required to reach pre-exercising concentrations was 48 h. In conclusion, endurance exercise in the horse decreases serum isoleucine, leucine, and valine concentrations, and increases serum alanine concentration. The decrease in serum branched-chain amino acid concentrations did not correspond to a measurable increase in total muscle branched-chain amino acid concentrations.

Drinking salt water enhances rehydration in horses dehydrated by frusemide administration and endurance exercise

Because the primary stimulus for thirst is an increase in plasma tonicity, we hypothesised that dehydrated horses would drink a greater total volume of fluid voluntarily during the first hour of recovery when they were initially offered salt water. To test this hypothesis, bodyweight (bwt), fluid intake (FI) and [Na+] were measured in 6 Arabian horses offered 3 rehydration solutions. After dehydration was induced by frusemide administration (1 mg/kg bwt, i.v.) followed by 45 km treadmill exercise, water (W), 0.45% NaCl and 0.9% NaCl were offered, in a randomised order, during the initial 5 min after completing exercise. Horses were subsequently placed in a stall and further intake of plain water during the first hour of recovery was measured. By the end of exercise, horses lost 5.2 +/- 0.2, 5.6 +/- 0.3 and 5.7 +/- 0.2% (P>0.05) bwt and FI during the first 5 min of recovery was 10.5 +/- 0.7, 11.6 +/- 0.8 and 11.6 +/- 1.5 l (P>0.05) for W, 0.45% NaCl and 0.9% NaCl, respectively. After 20 min of recovery, [Na+] had decreased with W but remained unchanged from the end exercise values for both saline solutions. During the initial hour of recovery, further water intake was 0.9 +/- 0.4, 5.0 +/- 0.5 and 6.9 +/- 0.7 l (P<0.05) for W, 0.45% NaCl and 0.9% NaCl, respectively. Therefore, total FI was 11.4 +/- 0.5, 16.6 +/- 0.7 and 18.5 +/- 1.7 l (P<0.05) for W, 0.45% NaCl and 0.9% NaCl, respectively, and persisting bwt loss after 60 min of recovery was greater (P<0.05) for W (3.5%) than for the 2 saline solutions (24% for 0.45% NaCl and 1.9% for 0.9% NaCl). In conclusion, providing salt water as the initial rehydration fluid maintained an elevated [Na+] and resulted in greater total FI and recovery of bwt loss during the first hour of recovery, in comparison to offering only plain water.

Effect of oral administration of electrolyte pastes on rehydration of horses

OBJECTIVE

To determine whether the composition of electrolyte pastes formulated for oral administration influences voluntary water intake (WI) by horses recovering from furosemide-induced dehydration.

ANIMALS

6 horses.

PROCEDURES

Voluntary WI, body weight, and blood and urine constituents were measured before and after induction of dehydration by furosemide administration and overnight withholding of water; these same variables also were measured during a 36-hour rehydration period. Each horse was evaluated 4 times with random application of 4 treatments (electrolyte pastes) that provided 0.5 g of KCl/kg of body weight, 0.5 g of NaCl/kg, 0.25 g of NaCl and 0.25 g of KCl/kg, or no electrolytes (control treatment). Electrolyte pastes were administered 3 times (4, 8, and 12 hours after start of the rehydration period).

RESULTS

Administration of all electrolyte pastes resulted in significantly greater voluntarily WI, compared with the control treatment, and was accompanied by significantly greater recovery of body weight when NaCl was a component of the paste. Administration of NaCl and NaCl-KCl pastes tended to produce a state of transient hyperhydration; however, electrolyte administration also resulted in significantly greater urine production and electrolyte excretion during the final 24 hours of the rehydration period. Adverse effects of oral administration of hypertonic electrolyte pastes were not observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of electrolyte pastes to dehydrated horses increases voluntary WI and improves rehydration during the rehydration period. Rehydration is more rapid and complete when NaCl is a component of the electrolyte paste.

Glycerol hyperhydration in resting horses

SUMMARY

To determine whether administration of glycerol-containing solutions induces a state of transient hyperhydration in resting euhydrated horses, changes in plasma and urine constituents were measured in four horses for 1 h before and 5 h after nasogastric administration of each of four treatments (Experiment 1). Treatments were applied in a randomized fashion and included: (1) 1.0 g.kg(-)(1)glycerol in 8 L of water (G); (2) 8 L of water (W); (3) 8 L of 0.9% NaCl solution (S); and (4) 1.0 g.kg(-)(1)glycerol in 8 L of 0.9% NaCl solution (GS). In a subsequent study, voluntary water intake was measured hourly for 5 h after nasogastric administration of each treatment (Experiment 2). All treatments produced mild plasma volume expansion ranging from 3.2 to 5.8% in Experiment 1. Administration of glycerol containing solutions increased serum glycerol concentration approximately 100-fold and plasma osmolality (P(osm)) by approximately 10 mOsm/kg and resulted in a tendency towards increased renal water conservation despite increased osmole excretion. In contrast, W treatment decreased plasma and urine osmolality and was accompanied by increased urine production and decreased renal water conservation. Plasma and urine osmolality, as well as renal osmole and water excretion, were unchanged after S administration. In Experiment 2, horses treated with GS voluntarily drank an additional 5.2 +/- 0.9 L of water during the initial hour following nasogastric administration of 8 L of solution. Voluntary water intake with the other treatments was less than 1.0 L for the entire 5 h observation period. Collectively, the results of both experiments suggest that administration of glycerol in saline would produce transient hyperhydration in resting euhydrated horses by enhancing renal water conservation and stimulating voluntary water intake.