SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
ELECTROLYTES
Post exercise concentrations of sodium, potassium and chloride in serum or plasma
are variable, and there seems to be little value in monitoring them following racing or
in response to training. Large amounts of each of these ions are lost in sweat during
endurance rides, however, determination of their plasma concentration provides no
guide to whole body sodium and potassium status. In some situations, measured
concentrations may actually increase despite the existence of sizable deficits, due to
the disproportionate loss of body water. Chloride is the primary anion in sweat, and
decreases in its concentration in plasma can be expected during and following
prolonged exercise. The higher the temperature and humidity and the longer the
distance, the more marked the hypochloremia. At times, the chloride deficit may be
reflected by the development of a hypochloremic metabolic alkalosis. Whole body
carbon dioxide levels do not necessarily increase, but the need to maintain
electroneutrality results in increases in plasma bicarbonate concentrations.
Replacement of the chloride deficit corrects the alkalosis. Calcium and magnesium
are other cations which may be lost in sweat.
It is unusual to observe
hypomagnesemia in endurance horses but hypocalcemia develops from time to time.
This may be associated with the development of a variety of clinical problems such
as muscle weakness, exertional rhabdomyolysis and synchronous diaphragmatic
flutter, particularly when coexisting with a metabolic alkalosis.
Resting inorganic phosphate concentrations tend to decrease with age and in
response to training. Variations of nutritional origin can also exist between horses
housed in different locations. Both maximal and submaximal exercise lead to
transient increases in plasma inorganic phosphate concentration. The magnitude of
the increase is variable. The origins of the increase have not been investigated,
probably because it is temporary and of no apparent clinical relevance.
Differences exist between the resting concentrations of sodium and potassium or
racehorses and endurance horses. Concentrations of these cations tend to be lower
in the latter group, for reasons which are not clear. Whether it reflects differences in
diet or is an effect of regular prolonged submaximal training bouts is not known. In
Thoroughbreds and Standardbreds, while no relationship has been demonstrated
between performance quality and exercise-induced changes in any plasma
constituent, two authors have claimed that the better athletes have higher resting
concentrations of sodium (139-143 mEq/L).
It has been reported that standardbreds race best when resting potassium values
range from 3.6 to 4.0 mEq/L. The same author felt that all horses with resting
concentrations above 4.8 mEq/L displayed abnormal T-waves in their
electrocardiograms. However, neither of these claims have been substantiated by
others.
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