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Body weight, fluid, electrolyte, and hormonal changes in horses 
competing in 50- and 100-mile endurance rides.
Department of Veterinary Clinical Sciences, College of Veterinary 
Medicine, Washington State University, Pullman 99164-6610, USA.

OBJECTIVE: To investigate effects of prolonged exercise on fluid and 
electrolyte losses in horses competing in 50- and 100-mile endurance 
competitions, with emphasis on recovery. ANIMALS: Changes in body 
weight (BW); PCV; serum osmolality; plasma total protein, lactate, 
aldosterone, and serum electrolyte concentrations; and exchangeable 
cation content were measured in 12 and 7 horses before and after and 
before, during, and after successful completion of 50- and 100-mile 
endurance rides, respectively. PROCEDURE: BW was measured by use of a 
portable load bar scale, and blood samples were collected during the 
hour before ride start, at ride finish, and after approximately 2 and 
18 hours (overnight) of recovery for horses competing in the 50-mile 
ride. For horses competing in the 100-mile ride, BW was measured and 
blood samples were collected at the start; after 50, 67, and 84 miles 
of the ride; at the finish; and after approximately 12 hours 
(overnight) of recovery. RESULTS: BW decreased by (mean +/- SEM) 3.6 
+/- 0.0% and 4.9 +/- 0.8% in horses that successfully completed rides 
of 50 and 100 miles, respectively. After the overnight recovery 
period, BW was 4.3 +/- 0.5% and 3.9 +/- 0.8% lower than preride 
values for horses performing the 50- and 100-mile rides, 
respectively. A decrease in plasma volume during the ride was 
reflected by an increase in plasma total protein concentration, but 
both measures returned to preride values after overnight recovery. 
Serum osmolality and serum electrolyte concentrations decreased and 
aldosterone concentration increased during prolonged exercise. 
Aldosterone concentration peaked after overnight recovery. 
CONCLUSION: Despite apparent rapid return of plasma volume and ionic 
composition to near normal values, substantial depletion of body 
fluid and electrolyte stores persists after an overnight recovery 
period in horses that successfully complete 50 or 100 miles of 
endurance competition.

Effects of electrolyte and glycerol supplementation on recovery from 
endurance exercise.
Department of Large Animal Clinical Sciences, Michigan State 
University, East Lansing 48824-1314, USA.

Incomplete recovery from endurance exercise after an overnight rest 
period is reflected by persisting weight loss and an elevated plasma 
aldosterone concentration, even in successful competitors. To 
determine whether supplementation with high doses of electrolytes, 
with or without glycerol, enhances recovery, the following were 
measured in 6 Arabian horses before and after completion of a 60 km 
treadmill exercise test simulating an endurance ride and after 12, 
24, 48, and 72 h of recovery: bodyweight; plasma osmolality; plasma 
concentrations of protein, electrolytes, aldosterone and cortisol; 
and urine and faecal electrolyte concentrations. Before and during 
the exercise test, horses were supplemented with a total of 2.4 ml/kg 
bwt of water (W); 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 ml/kg 
bwt of water (E); or 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 
ml/kg bwt (3 g/kg bwt) of glycerol (GE). Although weight loss after 
completion of the simulated ride was greater (P < 0.01) for W (3.2%) 
than for E and GE (1.0 and 0.9%, respectively), horses supplemented 
with E or GE experienced further weight loss by 24 h after the 
simulated ride (2.2 and 2.1% for E and GE, respectively) while 
bodyweight with W remained unchanged (3.0%) from the finish value. 
After 48 h of recovery, bodyweight was not different from the 
starting values with E and GE but remained decreased (P < 0.01) with 
W throughout the recovery period (2.2% persisting weight loss after 
72 h of recovery). Plasma osmolality and plasma Na+ and Cl- 
concentrations increased (P < 0.01) and plasma protein concentration 
decreased (P < 0.01) after the exercise test with E and GE but were 
unchanged with W. Plasma osmolality and protein and electrolyte 
concentrations returned to pre-exercise values within 12 h of 
recovery with the exception of a persistent increase in plasma Na+ 
concentration with GE. The greatest plasma aldosterone concentration 
was measured after 12 h of recovery with W (1357 pmol/l) and was 
greater (P < 0.02) than that with E and GE (24 and 304 pmol/l, 
respectively). Urine production during the simulated ride increased 
(P < 0.01) with GE and resulted in loss of approximately 20% and 
essentially 100% of supplemented Na+ and K+, respectively. In 
contrast, electrolyte losses in faeces were unaffected by electrolyte 
or glycerol supplementation. In conclusion, supplementation with high 
doses of electrolytes as hypertonic oral pastes attenuated weight 
loss during a simulated endurance ride (by enhancing voluntary water 
intake); however, it did not prevent development of significant 
weight loss during the initial 24 h of recovery. Glycerol 
administration resulted in no benefits, and actually increased urine 
electrolyte losses, in comparison to supplementation with electrolytes alone.

The effect of ambient temperature and saline loading on changes in 
plasma and urine electrolytes (Na+ and K+) following exercise.
Department of Animal Physiology, Swedish University of Agricultural 
Sciences, Uppsala, Sweden.

In this study 4 Standardbred geldings (age 3-8 years, weight 431-531 
kg) were used. The horses were fed a hay and oat diet and the total 
sodium intake was about 32 mg/kg bwt (690 mmol/day). An exercise test 
(ET) which contained 3 phases was performed. Phase I consisted of 
23.5 min of mainly submaximal exercise, Phase 2 of 2 h of box rest 
and Phase 3 of 26 min of exercise including an intensive trot over 
2600 m at 90% of VO2max. The ET was repeated 3 times: the first at 20 
degrees C (30-40% RH), the second at 35 degrees C (30-40% RH) and the 
third at 35 degrees C (30-40% RH) after a nasogastric administration 
of 10 litres of 0.9% NaCl solution (35 degrees C and saline load [+ 
F]). Blood samples were taken before, during and after exercise. To 
measure fluid loss, horses were weighted before and after the ETs. 
Total urine output was determined 2 days before the ET (control), 
throughout the exercise day and for 2 days after (recovery days). 
There were an increase in blood and rectal temperatures after both 
exercise phases and a significant higher blood temperature was 
observed after exercise at 35 degrees C compared to 20 degrees C. The 
horses lost about 2% of their bodyweight (bwt) during the ETs. The 
plasma protein concentration increased during the exercise phases and 
remained elevated 2 h after exercise at both 20 degrees C and 35 
degrees C, even though the horses had free access to water. The 
plasma protein concentration had returned to pre-exercise levels 26 h 
post exercise. After the saline load, total plasma protein 
concentration fell and increased only at the end of each exercise 
phase. The major mechanism regulating fluid balance after exercise 
seemed to be a lowered urinary excretion since water intake did not 
increase significantly. Urinary potassium excretion was positive 
throughout the experiment. During control days there was a positive 
sodium balance, shown by a urinary sodium excretion of 260 mmol/day. 
Post exercise urinary sodium excretion fell and remained very low 
until the second day of recovery, except after saline loading. In 
addition, plasma sodium was lowered 26 h after exercise at 35 degrees 
C. This study shows that with a daily salt intake of 38 g it will 
take several days to compensate for a sodium loss caused by sweating. 
Therefore, it is recommended that extra salt be given during the 
exercise day. In the experimental situation, pre-exercise saline 
supplementation was beneficial since the recovery time was shortened.

Restoration of water and electrolyte balance in horses after repeated 
exercise in hot and humid conditions.
Agricultural Research Centre, Ypaja, Finland.

Nine adult riding horses performed on a treadmill a competition 
exercise test (CET) and 24 h later a standardised exercise test (SET) 
at mean temperature 28 degrees C and relative humidity 58%. Each 
horse performed the tests 5 times at 2 week intervals. The horses 
were given isotonic glucose-electrolyte solution via a nasogastric 
tube 30 min after the CET, except after the last trial when water was 
given. Blood lactate, plasma concentration of aldosterone, arginine 
vasopressin, protein, sodium, potassium, chloride, magnesium and 
calcium were measured. Heart rate at blood lactate concentration 4 
mmol/l (PLa4) in the SET, plasma volume (PV) and red cell volume (CV) 
were determined. Mean weight loss after CET was 3.1% and did not 
change significantly during the study. Bodyweight loss (BWL2) before 
SET (-1.8% after the first trial) decreased linearly with time (P < 
0.05) and was -0.8% after the fourth trial. After the fifth trial, 
when only water was given, the weight loss was -2.5%. PLa4 correlated 
significantly (P < 0.001) with BWL2 when BWL2 was greater than -1.2%. 
The horses acclimated to exercise in hot and humid conditions as 
indicated by better recovery of bodyweight, increased PV, lower peak 
lactate concentrations and heart rate and attenuated decrease in the 
concentrations of sodium and chloride. It is concluded that changes 
in bodyweight provide a good indication of recovery of horses after 
exercise in hot and humid conditions; and administration of an 
isotonic glucose-electrolyte rehydration solution after exercise 
helps to overcome dehydration better than water alone.  

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