Endurance.Net Ridecamp Archives

Here are some interesting abstracts from Pub Med.  I think these show 
us what we already know -- that our horses like to drink the sponge 
water that's been sitting out in the sun ;-), and do better when we 
elyte them as they are drinking and eating or by putting the 
salt/elytes into their food and water, and that they benefit from 
post ride salt/elyte supplementation following rides.  Whew!   Karen

Rehydration fluid temperature affects voluntary drinking in horses 
dehydrated by furosemide administration and endurance exercise.
Department of Large Animal Clinical Sciences, College of Veterinary 
Medicine, D-202 Veterinary Medical Center, Michigan State University, 
East Lansing, MI 48824-1314, USA.

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.

Drinking salt water enhances rehydration in horses dehydrated by 
frusemide administration and endurance exercise.
Department of Large Animal Clinical Sciences, Michigan State 
University, East Lansing 48824-1314, USA.

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.

Strategies for voluntary rehydration in horses during endurance exercise.
Department of Medicine and Surgery, Swedish University of 
Agricultural Sciences, Uppsala, Sweden.

To avoid dehydration and a decrease in performance capacity in 
horses, fluid and electrolyte losses need to be compensated for 
during long distance rides as well as on other occasions when sweat 
losses are high during exercise. Thirteen endurance-trained horses, 
age 5-14 years, were used to compare 3 strategies of voluntary 
rehydration during prolonged exercise, offering 1) water, 2) water 
after administering salt paste (3 x 30 g of NaCl) per os and 3) 0.9% 
saline. The ride covered 62 km and consisted of 3 rounds, of 20, 22 
and 20 km, respectively. During the first 20 km, no fluid was offered 
to any of the horses. Thereafter, fluid was repeatedly offered from 
buckets at the 'vet gates' and at fluid stations situated in the 
middle of the rounds. Fluid intake and bodyweight were measured 
during the ride and up until 3 b after the ride. The low heart rates 
and unchanged plasma glucose concentration indicated that the work 
load was moderate. Total fluid intake was significantly higher in the 
saline group than in the water group or the salt paste group. The 
total plasma protein concentration (TPP) fell below resting values in 
the saline group post exercise, indicating an increase in plasma 
volume. No changes in TPP were seen in the other groups. Plasma 
sodium concentration during the ride increased in the salt paste 
group but not in the saline drinking horses despite their higher NaCl 
intake. The water group had an increased plasma aldosterone 
concentration post exercise, indicating that sodium-conserving 
mechanisms had been activated. Plasma potassium concentration 
decreased in all treatments from pre- to post ride. It was concluded, 
that drinking saline solution during and after exercise is a good 
strategy for rehydration since this group showed the fastest recovery 
of their bodyweight losses. The persistently elevated plasma sodium 
concentration in the salt paste group during the ride, is indicative 
of a disturbance in the fluid distribution between the body fluid 
compartments, which can be exacerbated by the low water intake. To 
give salt paste immediately before or during exercise is, therefore, 
not recommended.


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